JPS61208619A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the coefft. of friction and to improve durability by using cyclic isocyanate as a hardener component for a back coat layer. CONSTITUTION:A magnetic recording layer is provided on a nonmagnetic substrate and the back coat layer is provided on the opposite side thereof. The cyclic polyisocyanate is used as the hardener for a curable binder in the back coat layer. The binder to be used for the back coat layer is a resin having an active hydrogen group such as hydroxyl group and more particularly a rubber resin such as urethane prepolymer. The rubber binder is used at >=20wt%, more preferably 40-90wt% ratio. The hardener is the cyclic polyisocyanate which is the trimer of hexamethylene diisocyanate. The cyclic polyisocyanate is used at about 5-30wt% of the binder. While the durability is thereby improved, the coefft. of friction is decreased and the back coating layer is made additionally specular by increasing correspondingly the rubber binder. The improvement in the electromagnetic conversion characteristic is made possible as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention provides a magnetic recording medium with excellent electromagnetic conversion characteristics and good running durability.

[Background of the invention]

Currently, magnetic recording media are widely used5 in the fields of audio, video, magnetic disks, etc., and the amount of information recorded on magnetic recording media is increasing year by year. There is an increasing demand for media to have higher recording densities.

High coercive force and short wavelength recording have been proposed both theoretically and experimentally as one of the requirements for magnetic recording media for high-density recording. Along with this, methods such as using smaller magnetic particles and making the magnetic layer more mirror-finished are being adopted, and on the other hand, the pace is also moving toward mirror-finishing with fewer irregularities, which improves physical properties such as runnability and durability. It's having a negative impact.

Back coating is considered as one of the improvement methods, and various proposals have been made regarding the composition of the binder, inorganic filler, lubricant, etc. (for example, Japanese Patent Publication No. 57-2976
No. 9), running durability (shaving of back coat layer) adhesion,
At present, there is no satisfactory balanced electromagnetic conversion characteristic.

As higher performance is required in recent years, it is desirable to make the back coat layer mirror-finished as much as possible from the viewpoint of electromagnetic conversion characteristics. Moreover, as the magnetic layer becomes more mirror-finished, it is necessary to further reduce the friction caused by the back coat layer, and since it is used in a variety of environments, it is necessary to improve durability and improve adhesion by preventing dropouts. Must be. As a countermeasure to these problems, possible methods for reducing friction include the use of high molecular weight binders, reduction of rubber components, etc. However, high molecular weight binders have problems from the viewpoint of pigment dispersibility, and problems arise when reducing the rubber component from the viewpoint of adhesion.

[Purpose of the invention]

An object of the present invention is to provide a magnetic recording medium having a back coat layer with a small coefficient of friction and excellent durability.

Since the back coat layer has a small coefficient of friction, it can be mirror-finished, and a magnetic recording medium with excellent electromagnetic conversion characteristics can be obtained.

[Summary of the invention]

The magnetic recording medium of the present invention has a magnetic recording layer provided on a non-magnetic substrate and a back coat layer on the opposite side. It is characterized by using a cyclic polyisocyanate as the agent.

All polyisocyanates conventionally used as curing agents for curing polyurethane prepolymers and other binders containing resins having reactive groups such as active hydrogen are linear or branched. Since cyclic polyisocyanate is used in the present invention, it is possible to obtain a binder resin structure with a three-dimensional structure that is stronger than that obtained using conventional curing agents, increasing durability and reducing the coefficient of friction. By increasing the amount of the agent, it is possible to make the back coat layer mirror-like, and the electromagnetic conversion characteristics can also be improved.

[Detailed description of the invention]

The binder used in the back coat layer of the present invention is a resin having an active hydrogen group such as a hydroxyl group, and is particularly a rubber-based resin such as a urethane prepolymer.

Examples of resins that can coexist include vinyl chloride-vinyl acetate (containing several percent of vinyl alcohol) copolymer. More rubber-based binder improves adhesion to the supporting substrate, but increases the coefficient of friction.

However, according to the present invention, even if the amount of the rubber binder is large, it is possible to provide a back coat layer with a sufficiently low coefficient of friction. Vinyl chloride-vinyl acetate copolymer improves durability,
Decrease the coefficient of friction. However, if the amount is too large, the adhesiveness will be reduced, which will actually reduce the durability. Similarly, the surface roughness increases, which adversely affects the magnetic layer that is wound in contact with the magnetic layer on the surface side, and deteriorates the electromagnetic conversion characteristics. Therefore, the amount of the rubber binder is 20% by weight or more, preferably 4% by weight.
When used in a proportion of 0 to 90% by weight, a backcoat layer with good balance in all aspects of durability, surface roughness, coefficient of friction, and electromagnetic characteristics can be obtained.

The curing agent used in the present invention is a cyclic polyisocyanate, which is a pentamer of hexamethylene diisocyanate.

(CH2)6NGO O,N'',.

- etc. can be used. Examples of such polyisocyanates include Coronate EH and =rronate 2030 (manufactured by Nippon Polyurethane Kogyo Co., Ltd.). The cyclic polyisocyanate acts as a curing agent for the backcoat binder and is a polyurethane prepoly(polymer polyol).
and the hydroxyl group of the vinyl chloride-vinyl acetate copolymer to perform a curing reaction. The amount of cyclic polyisocyanate may be about 5 to 30% by weight depending on the binder formulation.

As will become clear later, when a cyclic polyisocyanate is used as a curing agent, the coefficient of friction and durability are greatly improved, so even if the amount of rubber binder is increased and the degree of mirror polishing is increased, the running performance will be maintained. In addition, mirror polishing reduces the influence on the magnetic layer and improves electromagnetic conversion characteristics.

For the back coat layer, conventionally known antistatic agents such as carbon black and dispersants 1. Ti01Fe 20s
, metal oxide powders such as ZnO, carbonates such as calcium carbonate, etc. can also be used.

Conventionally, the surface roughness K of the back coat layer is α05~
Although α of about 50 μm is often used, in the present invention, even if the surface is mirror-finished to a size of about 0.01 to [L20 μm, the friction is lowered by the use of cyclic polyisocyanate, so running performance and durability are not reduced. The preferred range of surface roughness is α02 to 115 μm. Mirror finish processing requires the use of a soft binder, but in the present invention, a large amount of rubber binder can be used, which not only increases mirror finish properties, but also improves adhesiveness and reduces dropouts. , the impact on durability is small.

For the magnetic layer, a conventionally proposed ferromagnetic alloy powder suitable for high-density recording is used, with % cobalt adsorption m,
A resin binder in which r -Fe2O3 or a ferromagnetic alloy powder having a specific surface area of 40 m2/l1 or more by the BET method is dispersed can be used. Further, the coercive force of the magnetic layer is preferably 1000 Oe or more.

Examples will be described below.

Magnetic layer cobalt adsorption γ-Fe20. 120 copies (
Long axis 14μ, short axis 105μ Hc 6 500s) Carbon black 5 parts (Mitsubishi carbon black MA-600 for antistatic use) (!-Al 20. Powder (cL5μ powder)
2 parts dispersant (soybean oil lecithin) 3 parts solvent MEK/) Luene 50150 100 parts The above composition is mixed in a ball mill for 3 hours to thoroughly wet the acicular magnetic iron oxide with the dispersant. Next, 15 parts of vinyl chloride vinyl acetate copolymer (VAGH manufactured by Union Carbide Co., Ltd.), 15 parts of thermoplastic urethane resin (Niraporan 2304 manufactured by Nippon Polyurethane Co., Ltd.), lubricant (5 parts of high-grade fat, solvent (MEK/), and luene) :50150) 20
Mix and dissolve 0 parts of the mixture well. This was put into the ball mill that had been subjected to the magnetic powder treatment and dispersed again for 36 hours. After dispersion, 5 parts of an isocyanate compound (Desmodur L manufactured by Bayer AG) capable of reacting with and crosslinking functional groups mainly composed of hydroxyl groups in the binder is added. This is 14
It is applied onto μ polyester film and passed through a magnetic field to orient the magnetic particles.

After drying, the surface is smoothed and heated at 60° C. for 47 hours to promote the crosslinking reaction of incyanate.

This is used as a magnetic layer.

Example (back coat layer) Carbon fiber 5y/RAVENlooo 1o
o part (Columbia Carbon Co., Ltd. 28 mμ) Tuboran 5033) Dispersant (soybean oil lecithin) 3 parts Solvent (ME
K/) Luene so, "so) soo part The ratio of vinyl chloride vinyl acetate copolymer and urethane prepolymer is as shown in Table 1. The above composition was heated in a ball mill to
After time dispersion, 1 hour of a cyclic isocyanate compound Coronae) EH or 2030 (manufactured by Nippon Polyurethane Co., Ltd.) that can react with and crosslink with functional groups mainly composed of hydroxyl groups in the binder.
Add 0 copies. Apply 0.5 to 2.0 mm of this on the opposite side of the previous magnetic layer.
Apply to 0μ and let dry. After surface treatment, 60
℃ for 48 hours to accelerate the crosslinking reaction of incyanate. This was cut into 1/2IIVc to obtain a video tape. The magnetic tapes with back coat layers cured with Coronet) EH are Examples 1 to 5 shown in Table 1, and the magnetic tapes with back coat layers cured with Coronet) 2030 are Examples 1 to 5 shown in Table 1. Examples 6-8. For comparison, conventional chain polyisocyanate (Coronet) L)
A back coat layer cured with branched polyisocyanate (Coronet HL) was prepared in the same manner (Comparative Examples 1 to 3).
5).

Table 1 shows the results of measuring the properties of the above tape, and FIG. 1 shows the relationship between the friction coefficient, binder component ratio, and curing agent. In addition, in FIG. 1, m combinations of urethane prepolymer ioo parts in the systems of Examples 1 to 5 are also shown.

As a result, when a cyclic isocyanate (Coquaternate EH, Coronet 2030) is used, the coefficient of friction decreases considerably, so the rubber component increases, surface workability improves, and durability is sufficient even when mirror-finished. It has been found that a magnetic recording medium can be obtained.

Note that in Example 1, when the urethane component is reduced, processability and surface properties are reduced. Furthermore, although the coefficient of friction is lowered, it is thought that the durability is reduced due to poor adhesiveness.

Note that each characteristic was measured as follows.

1) Cutoff (L171m, stylus force 111L1 x 2.5μ was used, which was determined by the 20-point average method from a chart obtained using a surface roughness Talystep (manufactured by TAYLOR-HOBSON). Based on the measurement data Areas that were found to be non-uniform were picked up and excluded from the uniform data.

2) CS/N Detsuki uses NY-8300 under the desk and sets TDKRef to 0.
This is the relative value when .

3) When a load was applied to a cylinder with a friction coefficient of 401 filφ on the inside of the back coat surface and rotated by ff (40 g), the load (T2) was read using a tension analyzer.

4) Durability: 150I with the back coat on the inside of a 20■φ cylinder
After 20 minutes, the backcoat surface was evaluated as ◎0Δ× based on the degree of scratches on the back coat surface.

[Brief explanation of drawings]

FIG. 1 is a plot of the coefficient of friction for each curing agent when the ratio of salt vinyl acetate copolymer and urethane prepolymer was changed.

Claims (5)

[Claims] (1) In a magnetic recording medium in which a magnetic recording layer is provided on a nonmagnetic substrate and a back coat layer is provided on the opposite side, a cyclic isocyanate is used as a curing agent component for a curable binder in the back coat layer. A magnetic recording medium characterized by using. (2) Surface roughness of back coat layer is 0.01 to 0.20
The magnetic recording medium according to claim 1, characterized in that μ. (3) The magnetic recording medium according to claim 1 or 2, wherein 20% or more of the curable binder component in the back coat layer is a rubber binder. (4) The magnetic recording medium according to claim 3, wherein the rubber binder is a urethane prepolymer. (5) The magnetic recording layer is made of a resin binder in which ferromagnetic alloy powder having a specific surface area of 40 m^2/g or more is dispersed by the BET method, and the coercive force of the magnetic layer is 1000 Oe.
A magnetic recording medium according to any one of claims 1 to 4, characterized in that the above is the case.