JPH06203362A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic transducing characteristics and durability of a coating type magnetic recording medium with an upper coating layer and a lower coating layer. CONSTITUTION:When a lower coating layer 2 and an upper coating layer 3 as a magnetic layer are formed on a nonmagnetic substrate 1 to obtain a magnetic recording medium, the glass transition temp. of resin contained in the lower coating layer 2 is set so that it is made lower than the glass transition temp. of resin contained in the upper coating layer 3 by >=10 deg.C. The lower coating layer 2 is formed with a coating layer contg. an arom. isocyanate curing agent and the upper coating layer 3 with a coating layer contg. an aliphatic isocyanate curing agent. The curing density and Young's modulus of the upper coating layer 3 become higher than those of the lower coating layer 2, satisfactory rigidity is ensured and durability is enhanced. Since the glass transition temp. of the lower coating layer 2 is low, surface smoothening is attained by calendering and electromagnetic transducing characteristics in a high frequency region are improved. The curing of the upper coating layer 3 is accelerated by the aliphatic isocyanate curing agent, the crosslinking density is increased, the falling of powder is suppressed and dropout is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium such as a magnetic tape or a magnetic disk, and is particularly configured to have excellent electromagnetic conversion characteristics, durability and reliability.

[0002]

2. Description of the Related Art In coating type magnetic recording media such as magnetic tapes and floppy disks, the development for increasing the recording capacity and the recording density has been earnestly pursued. Regarding the recording density of the coating type magnetic recording medium, the ferromagnetic powder contained in the magnetic layer is made to have a high Hc, the packing density of the ferromagnetic powder is increased, and
It is known that the thickness can be increased by reducing the thickness of the magnetic layer. However, when the magnetic layer is made thin, stress due to sliding friction between the magnetic head and the magnetic recording medium concentrates on the magnetic layer, and the durability of the magnetic layer tends to deteriorate. Therefore, an undercoat layer is provided between the non-magnetic support and the magnetic layer,
It has been practiced to improve the electromagnetic conversion characteristics by improving the durability of the magnetic recording medium or imparting magnetism to the undercoat layer.

Further, JP-A-2-105326 and JP-A-3-216812 disclose a coating type magnetic recording medium composed of two magnetic layers and an undercoat layer.
It has been shown that the Tg (glass transition point) of the upper layer polyurethane resin is made higher than the Tg of the lower layer polyurethane resin to improve electromagnetic conversion characteristics and running durability.

[0004]

When the resin layer having a high Tg is placed on the surface layer side of the magnetic recording medium, the resin having a high Tg has a higher Young's modulus, so that the surface layer of the magnetic recording medium is It becomes harder and can be more durable in a high temperature environment.

However, a resin having a high Tg reacts slowly with the isocyanate group of the curing agent, and it takes a considerable time for the reaction to proceed sufficiently. For this reason, there is a tendency that powder is dropped due to insufficient curing reaction, that is, a large amount of powder mixed with the resin coating is released, and the number of dropouts is increased.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide a magnetic recording medium in which dropout is reduced and durability is further improved.

[0007]

Therefore, in the present invention, in a magnetic recording medium comprising an undercoat layer on a non-magnetic support and an overcoat layer as a magnetic layer in this order, a resin contained in the undercoat layer. Is set to be 10 ° C. or more lower than the Tg of the resin contained in the overcoat layer, the undercoat layer is formed by a coating layer containing an aromatic isocyanate curing agent, and the overcoat layer is formed with an aliphatic isocyanate curing agent. It is formed by a coating layer containing.

Further, the film thickness of the overcoat layer is set to 0.1 μm or more and 1.0 μm or less.

[0009]

Therefore, since the Tg of the resin contained in the overcoat layer is set to be higher than the Tg of the resin contained in the undercoat layer, the Young's modulus of the overcoat layer becomes high and sufficient rigidity can be obtained even in a high temperature environment. Increases durability. In addition, T of the undercoat layer
Since g is lower than Tg of the overcoat layer by 10 ° C. or more,
The smoothness of the surface is improved by the calendar processing, and the electromagnetic conversion characteristics in the high frequency range are improved.

Further, as the isocyanate curing agent, an aliphatic type is more reactive than an aromatic type, but since the aliphatic isocyanate curing agent is used in the overcoat layer, a high T
g The curing of the resin is accelerated and the crosslink density is increased. As a result, less powder is dropped and dropout is greatly reduced.

Further, the topcoat layer as the magnetic layer is set to be as thin as possible within the range where a uniform coating film can be obtained in order to increase the recording density.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording medium of the present invention is shown in a sectional view in FIG.
As shown in, the undercoat layer 2 is formed on the non-magnetic support 1, and
The top coat layer 3 which is a magnetic layer is laminated.

As the non-magnetic support 1, a film made of cellulose diacetate, cellulose triacetate, polyvinyl chloride, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyamide, polyimide or the like is used.

The undercoat layer 2 is composed of inorganic powder, carbon black, a lubricant and a binder.

The top coat layer 3, which is a magnetic layer, is composed of metal magnetic powder, alumina, carbon black, a lubricant and a binder.

The inorganic powder contained in the undercoat layer 2 contains Fe.
Fine powders of OOH, alumina, chromium oxide, α-iron oxide, titanium oxide, silica and the like are used.

Lubricants contained in the undercoat layer 2 and the overcoat layer 3 include fatty acids, fatty acid esters, phosphate esters,
A plurality of fluorine-based hydrocarbons and the like are used in combination.

As the binder contained in the undercoat layer 2 and the overcoat layer 3, a system in which vinyl chloride-vinyl acetate-vinyl alcohol copolymer, nitrocellulose, polyurethane resin, polyester resin are appropriately combined is used, and a curing agent is used. Is used together with an isocyanate compound.

These materials are made into a coating material by a dispersing machine such as a pressure kneader, a planetary mixer, a ball mill, a sand mill, a pebble mill together with a mixed solvent in which methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, cyclohexanone, and acetone are appropriately combined to prepare a magnetic coating material. Is coated on one side or both sides of the non-magnetic support 1 and dried to form a magnetic recording medium. Further, if necessary, the non-magnetic support 1
A back coat layer made of carbon black, inorganic powder, resin, curing agent, lubricant or the like may be provided on the side opposite to the side provided with the magnetic layer.

In order to form a two-layer coating layer on the non-magnetic substrate 1, the topcoat paint is applied after the undercoat paint has been applied and dried. The thickness of the overcoat layer 3 which is a magnetic layer is set so that the thickness after drying is 0.1 μm or more and 1.0 μm or less.

In the magnetic recording medium of the example, as the coating material for the undercoat layer 2, the solid content of the following composition was mixed with a mixed solvent consisting of MEK, toluene and cyclohexanone to form a coating material having a solid content concentration of 35% by weight. Then, this is mixed and dispersed in a sand mill for 3 hours, and then coated on a non-magnetic support 1 (polyethylene terephthalate film) having a thickness of 62 μm so that the film thickness after drying is 1.0 μm and dried to form an undercoat layer 2 Was formed.

Α-iron oxide (particle size 0.06 μm) 57.0% by weight carbon black 13.0% by weight MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 10.0% by weight polyurethane resin (Tg 0 C) 10.0 wt% oleic acid 0.6 wt% n-butyl stearate 1.8 wt% butoxyethyl stearate 1.8 wt% oleyl oleate 1.8 wt% Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) ( Aromatic isocyanate curing agent) 4.0% by weight Next, as a coating material for the overcoat layer 3, a solid content of the following composition is mixed with a mixed solvent consisting of MEK, toluene, and cyclohexanone to obtain a solid content concentration of 35% by weight. A paint is formed, and the mixture is mixed and dispersed by a sand mill for 3 hours, so that the film thickness after drying becomes 0.3 μm on the undercoat layer 2 previously formed. Cloth and then dried to form a top coat layer 3.

Metal magnetic powder (Hc: 1700 Oe, BET: 40 m ² / g) 63.0 wt% carbon black 2.0 wt% alumina 11.0 wt% MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 7.5% by weight Polyurethane resin (Tg 40 ° C.) 7.5% by weight Oleic acid 0.6% by weight n-Butyl stearate 1.8% by weight Butoxyethyl stearate 1.8% by weight Oleyl oleate 1.8% by weight Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.) (aliphatic isocyanate curing agent) 3.0% by weight The magnetic sheet thus obtained was subjected to a supercalendering treatment and heat treatment at 60 ° C. for 24 hours, and then 3.5. Punch it into a 1-inch disc, then add 1
Polishing was performed with a No. 0000 polishing tape for 10 seconds.

In order to compare with the characteristics of the magnetic recording medium of this example, a sample of the comparative example was prepared as follows.

(Comparative Example 1) As a paint for the undercoat layer 2,
The solid content of the following composition was mixed with a mixed solvent consisting of MEK, toluene and cyclohexanone to give a solid content of 35
A coating material having a weight percentage of 1% was formed, and the coating material was mixed and dispersed in a sand mill for 3 hours, and then dried on a nonmagnetic support 1 (polyethylene terephthalate film) having a thickness of 62 μm to have a film thickness of 1.
The undercoat layer 2 was formed by coating so as to have a thickness of 0 μm and drying.

Α-iron oxide (particle diameter 0.06 μm) 57.0 wt% carbon black 13.0 wt% MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 10.0 wt% polyurethane resin (Tg 50 C) 10.0 wt% oleic acid 0.6 wt% n-butyl stearate 1.8 wt% butoxyethyl stearate 1.8 wt% oleyl oleate 1.8 wt% Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) ( Aromatic isocyanate curing agent) 4.0% by weight Next, as a coating material for the overcoat layer (magnetic layer) 3, the solid content of the following composition was mixed with a mixed solvent consisting of MEK, toluene, and cyclohexanone to obtain a solid content concentration. After forming 35% by weight of the paint and mixing and dispersing the paint in a sand mill for 3 hours, the film thickness after drying on the undercoat layer 2 becomes 0.3 μm. Coated and dried to form an overcoat layer 3.

Metal magnetic powder (Hc: 1700 Oe, BET: 40 m ² / g) 63.0% by weight carbon black 2.0% by weight Alumina 11.0% by weight MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 7.5% by weight Polyurethane resin (Tg 40 ° C.) 7.5% by weight Oleic acid 0.6% by weight n-Butyl stearate 1.8% by weight Butoxyethyl stearate 1.8% by weight Oleyl oleate 1.8% by weight Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.) (aliphatic isocyanate curing agent) 3.0% by weight The magnetic sheet thus obtained is subjected to a super calender treatment and heat treated at 60 ° C. for 24 hours, and then 3.5 inches. Punched into a disc. In addition, this disk 1
Polishing was performed for 10 seconds with a No. 0000 polishing tape, and this was used as a sample of Comparative Example 1.

Comparative Example 2 Undercoating layer 2 was formed under the same conditions as in Comparative Example 1 except that the following composition was used as the solid content of the coating material for undercoating layer 2.

Α-iron oxide (particle diameter 0.06 μm) 57.0 wt% carbon black 13.0 wt% MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 10.0 wt% polyurethane resin (Tg 30 C) 10.0 wt% oleic acid 0.6 wt% n-butyl stearate 1.8 wt% butoxyethyl stearate 1.8 wt% oleyl oleate 1.8 wt% Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) ( Aromatic isocyanate curing agent) 4.0% by weight Next, the following composition was used as the solid content of the coating material for the overcoat layer 3, and the undercoating of the overcoat layer 3 was performed under the same conditions as in Comparative Example 1 except for the above. Formed on layer 2.

Metal magnetic powder (Hc: 1700 Oe, BET: 40 m ² / g) 63.0% by weight carbon black 2.0% by weight Alumina 11.0% by weight MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 7.5% by weight Polyurethane resin (Tg 40 ° C.) 7.5% by weight Oleic acid 0.6% by weight n-Butyl stearate 1.8% by weight Butoxyethyl stearate 1.8% by weight Oleyl oleate 1.8% by weight Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.) (aliphatic isocyanate curing agent) 3.0% by weight The magnetic sheet thus obtained was subjected to the same treatment as in Comparative Example 1 to form a sample of Comparative Example 2.

Comparative Example 3 Undercoat layer 2 was formed under the same conditions as in Comparative Example 1 except that the following composition was used as the solid content of the coating material for undercoat layer 2.

Α-iron oxide (particle size 0.06 μm) 57.0% by weight carbon black 13.0% by weight MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 10.0% by weight polyurethane resin (Tg 0 C.) 10.0 wt% oleic acid 0.6 wt% n-butyl stearate 1.8 wt% butoxyethyl stearate 1.8 wt% oleyl oleate 1.8 wt% Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.) ( Aliphatic isocyanate curing agent) 4.0% by weight Next, the following composition was used as the solid content of the coating material for the overcoat layer 3, and the undercoating of the overcoat layer 3 was performed under the same conditions as in Comparative Example 1 except for the above. Formed on layer 2.

Metal magnetic powder (Hc: 1700 Oe, BET: 40 m ² / g) 63.0 wt% carbon black 2.0 wt% alumina 11.0 wt% MR-110 (manufactured by Zeon Corporation) (Tg 70 ° C.) 7.5% by weight Polyurethane resin (Tg 40 ° C.) 7.5% by weight Oleic acid 0.6% by weight n-Butyl stearate 1.8% by weight Butoxyethyl stearate 1.8% by weight Oleyl oleate 1.8% by weight Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) (aromatic isocyanate curing agent) 3.0 wt% The magnetic sheet thus obtained was subjected to the same treatment as in Comparative Example 1 to form a sample of Comparative Example 3.

The physical properties (Tg of resin, Young's modulus, gel fraction) and the type of curing agent used in each sample of the above Examples and Comparative Examples 1 to 3 are shown in the table of FIG. The Tg of the mixed resin is represented by the sum of the Tg of each resin alone multiplied by the weight fraction. The Young's modulus is
It is obtained from the tensile test of the top coat film and the under coat film, and the gel fraction is calculated from the tetrahydrofuran extraction of the coat film.

Further, each of these samples was assembled in a 3.5 inch floppy disk case, and electromagnetic conversion characteristics by FDD and continuous durability test were measured. The measurement results are shown in the table of FIG. FD-1331 manufactured by NEC was used for the FDD for measurement, and the high frequency output of each sample was measured. Durability is temperature 5 ℃, relative humidity 35
%, The magnetic head is placed on the track 48, and the average reproduction output from 0 to 96 tracks is 50% of the initial output.
The amount of passes traveled until reaching the endurance time was measured, with the endurance time being the time until the end time decreased. In addition, the missing pulses of all the tracks after 1.5 million passes were measured, and the track with a signal pulse of less than 60% was determined as a defective track.
Dropout was evaluated by the number of defective tracks.

As shown in the results of FIGS. 2 and 3, in the magnetic recording medium of the example, the T content of the resin contained in the overcoat layer 3 was reduced.
Since g is higher than Tg of the resin contained in the undercoat layer 2, the curing density of the overcoat layer 3 is higher than that of the undercoat layer 2,
Since the Young's modulus of the upper coating layer 3 is higher than that of the lower coating layer 2, the surface layer becomes hard. On the other hand, since the inside is softer than the surface layer, the stress caused by friction with the magnetic head is relaxed,
As a result, durability is improved. Further, the gel content of the overcoat layer 3 is high, and the lubricant contained in the resin does not easily diffuse and gradually migrates to the surface over a long period of time, which also contributes to the improvement of durability. There is.

Further, since the undercoat layer 2 has a low Tg, a smooth surface can be obtained by the calendering process, so that the output in the high range is also high.

Further, in the magnetic recording medium of the embodiment, since the aliphatic isocyanate curing agent having higher reactivity than the aromatic type is used as the curing agent for the overcoat layer 3, the curing reaction of the overcoat layer 3 is sufficient. Has been done to. Therefore, there is no powder drop and the dropout is greatly reduced, showing excellent reliability.

On the other hand, when the Tg of the resin of the overcoat layer 3 is lower than the Tg of the resin of the undercoat layer 2 as in Comparative Example 1, the Young's modulus of the coating film is reversed and the Young's modulus of the undercoat layer 2 is high. Nevertheless, the curing reaction has not progressed. For this reason, the undercoat layer 2 is deformed, and the durability is not preferable.

Further, as in Comparative Example 2, even if the Tg of the resin of the overcoat layer 3 is higher than the Tg of the resin of the undercoat layer 2, if the difference is slight, the curing reaction of the undercoat layer 2 becomes insufficient,
Durability is low. In order to satisfy the durability and the reliability, it is necessary to set the difference between the Tg of the overcoat layer resin and the Tg of the undercoat layer resin to 10 ° C. or higher.

Further, as in Comparative Example 3, the Tg of the resin of the overcoat layer 3 is higher than the Tg of the resin of the undercoat layer 2, and the difference is 1
Even if the temperature is 0 ° C. or higher, if an aromatic curing agent is used for the topcoat layer 3 and an aliphatic curing agent is used for the undercoat layer 2, curing of the undercoat layer 2 proceeds before the curing treatment, so that the surface is smoothed by calendering. The surface cannot be obtained, and the output in the high frequency range is reduced.
Further, the undercoat layer 2 has a small Young's modulus although a sufficient curing reaction has proceeded, and since the difference from the Young's modulus of the overcoat layer 3 is large, the undercoat layer 2 is destroyed at the interface between the overcoat layer and the overcoat layer and durability is improved. bad. Further, since the overcoat layer 3 is insufficiently cured, powder is removed, a large number of defective tracks occur, and reliability is extremely low.

As is clear from comparison with such a comparative example,
In the magnetic recording medium of the example, the Tg of the undercoat layer 2 is set lower than the Tg of the overcoat layer 3 by 10 ° C. or more, the undercoat layer 2 is cured with an aromatic isocyanate curing agent, and the overcoat layer 3 is cured with an aliphatic isocyanate. Curing by the agent provides excellent electromagnetic conversion characteristics, high durability and high reliability with low dropout.

Further, the film thickness of the overcoat layer 3 is preferably made thinner in order to increase the recording density, and is set to 0.1 μm or more and 1.0 μm in consideration of the practical range in which a uniform coating film can be formed. .

[0044]

As is apparent from the above description of the embodiments, the magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics and durability, less dropouts, and extremely high reliability.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a magnetic recording medium according to an embodiment of the present invention,

FIG. 2 is a table showing physical properties of magnetic recording media in Examples and Comparative Examples,

FIG. 3 is a table showing characteristics of magnetic recording media in Examples and Comparative Examples.

[Explanation of symbols]

 1 non-magnetic support 2 undercoat layer 3 topcoat layer

Claims (2)

[Claims] 1. A magnetic recording medium comprising an undercoat layer on a non-magnetic support and an overcoat layer as a magnetic layer in this order, wherein the Tg of a resin contained in the undercoat layer is contained in the overcoat layer. Lower than the Tg of the resin to be treated by 10 ° C. or more, the undercoat layer is formed by a coating layer containing an aromatic isocyanate curing agent, and the topcoat layer is formed by a coating layer containing an aliphatic isocyanate curing agent. And a magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the film thickness of the overcoat layer is 0.1 μm or more and 1.0 μm or less.