JPH01118213A - magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium used as a magnetic tape or a floppy disk, and particularly to a magnetic recording medium with improved durability.

Conventional technology In recent years, magnetic recording media have achieved higher recording densities by improving magnetic properties by making magnetic powder particles finer and by adopting metal magnetic powder, etc., and by smoothing the surface of the magnetic layer to improve recording and reproducing performance. I've been doing it. In order to improve the smoothness of the surface of the magnetic layer, it is necessary to improve the dispersion of the magnetic powder in the binder.

Examples of these prior art include, for example, the Special
Publication No. 7, Japanese Patent Publication No. 58-41565, Japanese Patent Application Publication No. 1983
-238309 etc. are known. These methods include a polar group such as a sulfonic acid metal base in the binder resin molecules in the magnetic layer. Examples of resins containing polar groups include copolymer resins mainly composed of vinyl chloride containing sulfonic acid metal bases and carboxyl groups, which have a glass transition point (T
Hard resins with q) exceeding 50°C and polyurethane resins having sulfonic acid metal bases have been proposed. This polyurethane resin is obtained by expanding a polyhydroxy compound and a polyisocyanate, and a polyester polyol having a sulfonic acid metal base is used as the polyhydroxy compound, and this molecule contains a sulfonic acid metal base. Contains isophthalic acid and terephthalic acid.

Schifnirmethane diisocyanate is mainly used as a polyisocyanate compound, and since it contains many aromatic rings in the molecule, it is a hard resin with a high specific softness Tq among polyurethane resins.

In addition, nitrocellulose resin is known as another binder resin that can enhance the dispersibility of magnetic powder, but this also has Tq
It is a hard resin with a temperature exceeding 100°C.

For magnetic recording media, it is necessary to apply calendering as a mirror finishing step after coating and drying a magnetic paint on a non-specific support. Furthermore, as a method of improving the smoothness of the surface of the magnetic layer, a method of increasing the temperature and pressure in this step is being considered.

Problems to be Solved by the Invention However, in the above configuration, polyethylene terephthalate (PET), which is commonly used during calendering in the mirror finishing process, is used as a resin for dispersing and bonding magnetic powder, which has a high Tq. ) The temperature and pressure must be high enough to cause deformation of the film support. In this case, uneven stretching, deformation, and unevenness occur in the tape as a magnetic recording medium, making it impossible to obtain high electromagnetic conversion characteristics and causing problems in running performance. Furthermore, even if the magnetic layer exhibits sufficient smoothness, the magnetic layer binder resin is hard, making it brittle, leading to problems such as powder falling off at the interface with the head and increasing the amount of wear on the head. It had In particular, nitrocellulose resin has an excessively high Tq, which further exacerbates the above-mentioned drawbacks.

In view of the above problems, the present invention maintains high dispersibility of magnetic powder, facilitates calendering, provides high smoothness of the magnetic layer, and has excellent durability with less powder falling and head wear. The present invention provides a magnetic recording medium.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention comprises:
A magnetic layer in which ferromagnetic powder is dispersed in a binder is formed on a non-magnetic support.
Sulfonic acid metal base.

It contains a resin having at least one kind of polar group among carboxyl group and amino group and having Tq of 60°C or higher.

Effect of the present invention With the above configuration, the polar groups of the hard resin with a Tq of 50°C or more that have polar groups on the magnetic powder are strongly adsorbed, and at the same time a high degree of dispersion is maintained. The part of the hard resin that does not have a polar group (the part that is not adsorbed to the magnetic layer) and the soft resin with a Tq of 0°C or less are partially compatible with each other, resulting in a magnetic layer that serves to bind the whole. This can be calendered at low temperatures and pressures, forming a magnetic layer with low surface roughness, and the magnetic medium itself will not be deformed or elongated. In addition, the magnetic layer itself has a large tensile rupture characteristic, which reduces the phenomenon of powder falling off at the interface with the head and reduces the amount of wear on the head, thereby solving the conventional problems.

Example A magnetic tape according to an embodiment of the present invention will be described below.

Table 1 shows the results of evaluating the magnetic layer compositions of the magnetic tapes in Examples and Comparative Examples of the present invention, the mirror polishing calendaring conditions in the tape forming process, and the performance after forming the tapes.

MR manufactured by Teijin Ltd., which is a polyethylene terephthalate (PET) film with a thickness of 1 μm, which serves as the former non-magnetic support.
On one side of the film, a magnetic paint with the composition shown in the upper part of Table 1 made using a mixer and a sand mill was applied using the gravure coating method so that the thickness of the magnetic layer was 3 μm, oriented, dried, mirror-finished, and then cured. Then, a magnetic layer was provided. The mirror finishing calendering conditions are shown in Table 1. Further, on the side opposite to the magnetic layer, a back coat layer with a thickness of 0.6 μm, which is made by dispersing fine particles mainly composed of carbon black powder in a binder containing nitrocellulose resin and polyurethane resin, is provided and slit to form an 8Illff+video deck. A videotape was obtained.

The average roughness and tensile breaking strength of the magnetic layer surface of each of the obtained tapes were measured, and a 90-minute (P6-9o) length tape was wound into a cassette half and a 8-round video deck MVS-5000
The results of evaluating the tape performance using the above are shown in the lower part of Table 1.

Compositions A to D in Table 1 show examples of the present invention, and compositions E and G show comparative examples. The ferromagnetic alloy powder is a fine particle manufactured by Dowa Mining Co., Ltd. whose main component is IRE, which exhibits the following performance.

Resin (2) having a polar group and having a Tq of 50'c or more is a copolymer resin with a Tq of 69°C manufactured by Nippon Zeon Co., Ltd. and containing vinyl chloride as a main component having a sulfonic acid metal base in the molecule. ■ is manufactured by Sekisui Chemical Co., Ltd. and has a Tq of 66, whose main component is vinyl chloride with a carboxyl group in the molecule.
°C copolymer resin S-LeCE-C110. ■
is manufactured by Toyobo Co., Ltd. and contains nurphonic acid metal base as sodium sulfophthalic acid and has a Tq of 73 to 77°C.
Polyurethane resin pylon UR-8200. T
Polyurethane resins with q of 0°C or less @, ■ do not have sulfonic acid metal bases or carboxyl groups in the molecule,
@ is manufactured by Dainippon Ink & Chemicals Co., Ltd. Tq is -25~
-20°C bandex. (2) is N-2304 resin manufactured by Nippon Polyurethane Industries Co., Ltd. and having a Tq of 123°C. ■ contains a sulfonic acid metal base in the molecule, but ■
Polyurethane resin pylon UR with a Tq of 21 to 25°C manufactured by Toyobo Co., Ltd. with a low amount of phthalic acid and a low amount of phthalic acid.
-8300. ■ is Takeda Pharmaceutical Co., Ltd., which mainly reacts with diphenylmethane diisocyanate and butanediol adipaste, which does not contain sulfonic acid metal bases or carboxy/'M in the molecule, and increases the amount of urethane bonds by combining with other glycols. Co., Ltd. Tq is 24 ~
It is a polyurethane resin bamboo rack at 27°C. ■ is T made by Sekisui Chemical Co., Ltd. whose main component is vinyl chloride that does not contain sulfonic acid metal bases or carboxyl groups in the molecule.
The copolymer resin 5-LecA has a g of 66 to 68°C.

The isocyanate compound is Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd. The isocyanate compound is mixed immediately before applying the magnetic paint.

A tape having the magnetic layer composition and structure as described above was evaluated. When the calendering conditions are the same, the average surface roughness of the magnetic layer in the embodiment of the present invention is a small value;
C/, N (This is a measurement of the relationship between the 55 MHz signal output and the 4.5 MHz noise, expressed as a relative ratio when the initial value of Comparative Example E at room temperature is taken as odB.) and dropout. (D, o,) Performance leads to good results.

D, 0. is -1edB and 3tts-10dB in 16μs
Defects were measured after being regenerated for 15 minutes and expressed as the number of defects per minute. In the evaluation results at normal temperature and normal humidity, the examples are superior to the comparative examples. Next, in an environment of 40'0801 vs. humidity, a cassette half (Pa-90) with a tape wrapped in it was installed in an 8111111 video deck, the signal was recorded, the playback was run for 100 passes (150 hours), and then the performance was tested at room temperature. evaluated. C is comparative example E at normal temperature and humidity at the initial stage.
It is a relative ratio when the value of is set to OdB. The condition of the head was observed using a microscope. In the comparative example, powder adhesion (powder falling) and head clogging occurred near the gap of the head and on the glass portion, leading to a worsening of the CI/N and an increase in fi D, O,. In the example, the C/N was poor, but the characteristics did not deteriorate. The amount of head wear in the example was also small and excellent. This is a physical property of tensile strength at break (the magnetic layer peels off from the PET film,
This was achieved by a high value of the load required to cause cracking and fracture, and a small average surface roughness of the magnetic layer. In Comparative Example G, the dispersion of magnetic powder reached a high level, but
It was not possible to reduce the surface roughness unless the mirror finishing conditions were increased. This seems to cause deformation of the PET film, causing large variations in the measurement results.

Effects of the Invention As described above, according to the present invention, the binder of the magnetic layer contains T having at least one polar group among a sulfonic acid metal base, a carboxyl group, an amino group, and a sulfonic acid group in its molecule.
By containing a resin with a q of 50°C or higher and a polyurethane resin with a Tq of 0'C or lower, the magnetic powder can be dispersed well, the mirror workability is excellent, and the average surface roughness of the magnetic layer can be reduced. is small, the tensile modulus can be increased, and a magnetic recording medium with excellent durability can be obtained.

Claims (1)

[Claims] A magnetic recording medium in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is formed on a non-magnetic support, the binder containing a polyurethane resin having a glass transition point of 0° C. or lower, and 1. A magnetic recording medium comprising a resin having at least one polar group selected from sulfonic acid groups, sulfonic acid metal bases, carboxyl groups, and amino groups and having a glass transition point of 50° C. or higher.