JP2981241B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to an improvement in a binder thereof.

[Conventional technology]

The coating type magnetic recording medium has a structure in which a magnetic layer in which magnetic fine particles are dispersed in a binder is provided on a non-magnetic support. In order to improve the recording density of this coating type magnetic recording medium, the use of finer magnetic particles has been advanced. As the fine magnetic particles become finer, the dispersibility of the particles in the binder decreases, and the electromagnetic conversion characteristics of the magnetic recording medium do not improve as expected. To solve this problem, a resin having a polar group include -SO ₃ M, etc., a magnetic recording medium having a glass transition temperature no polar group is used in combination 25 ° C. or more resins as a binder has been proposed (JP-A 1-146121
issue). Although this magnetic recording medium has improved electromagnetic conversion characteristics, there remains a problem that durability cannot be sufficiently secured.

[Problems to be solved by the invention]

The present invention solves the problem of poor dispersion of the particulate metal magnetic powder in the binder, which the conventional product had,
Accordingly, it is an object to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and durability.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above problems, And at least one of a vinyl chloride resin having an -OH group, the combined use of a polyurethane resin having -SO ₃ M as a binder component, also a BET specific surface area of 48m ² / g or more fine metal magnetic powder It was found that it could be sufficiently dispersed.

The content of -SO ₃ M in the polyurethane resin, 1,000 ppm or more in terms in S content, less than 3,000ppm is a valid dispersibility particulate metal magnetic powder, the vinyl chloride-based resin -
SO ₃ M content should be 1,000 ppm or more and less than 3,000 ppm in terms of S content If the content of P is 500 ppm or more and less than 3,500 ppm in terms of the amount of P, the dispersion of fine metal magnetic powder was effective.

In order to improve the durability of the magnetic layer, the amount of vinyl chloride resin used is in the range of 5.0 to 7.5% by weight, based on the ratio of the amount of Cl in the vinyl chloride resin to the amount of Fe in the fine metal magnetic powder (Cl / Fe). Is more preferred.

However, to improve the durability, it was not sufficient to limit the amount of the vinyl chloride resin used. As a result of studying the cause, a phenomenon similar to the so-called head clogging occurs in which the low molecular weight resin remaining in the magnetic layer accumulates in the recording head portion of the recording machine. It has been found that it is preferable to include 1.0 to 2.5% by weight of a hydroxyl group and 0.02% by weight of a hydroxyl group in a polyurethane resin to improve the crosslinkability by a polyisocyanate compound.

The vinyl chloride resin used in the present invention, for example, Nippon Zeon Co., Ltd., MR 110 or conventional vinyl chloride-based _{resin,, C-CH 2 CH 2} SO 3 M, Such as those modified by introducing a compound having a polar functional group and chlorine into the molecule by a dehydrochlorination reaction, or a hydroxyl group-containing vinyl monomer such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, or 3-chloro- 2-hydroxypropyl acrylate and the like, and -SO ₃ M-containing monomer such as 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, vinylsulfonic acid and the like or Containing monomers, for example, methacrylic acid-3-chloro-2
-A resin obtained by copolymerizing propyl phosphate, 3-chloro-2-propyl acrylate, methacrylic acid-2-ethyl phosphate, and the like with vinyl chloride can be used.

The polyurethane resin -SO ₃ M-containing polyester diol, for example, 5-sodium sulfoisophthalic acid,
A hydroxyl group-containing polyurethane resin synthesized by using 2-potassium sulfoisophthalic acid and triol as a chain extender and combining it with a conventionally known polyester diol, diisocyanate and a diol type chain extender is used.

In the magnetic layer of the present invention, conventionally known abrasives such as alumina and red iron oxide, antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, and silicone oil may be mixed and dispersed.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 α-Fe (axial ratio: 1:10, S _BET : 52 m ² / g) 80 parts by weight Vinyl chloride resin (manufactured by Zeon Corporation, MR110) 10 parts by weight Polyurethane resin (OH content, 0.03 wt%) , S: 1,200pp
m, Tg: 20 ° C) 6 parts by weight Alumina 4.8 parts by weight Bengala 3.2 parts by weight Carbon black 2.0 parts by weight Myristic acid 3.2 parts by weight n-butyl stearate 1.2 parts by weight Toluene 102.5 parts by weight Cyclohexanone 102.5 parts by weight After stirring, the mixture was dispersed with a sand grind mill to obtain a dispersion. 4.0 parts by weight of the polyisocyanate compound and 35 parts by weight of toluene were added to this dispersion, mixed, stirred, and filtered to obtain a magnetic paint. The magnetic paint is applied and dried on a 10.0 μm-thick polyester film while performing a magnetic field orientation treatment so that the coating thickness after drying becomes 2.5 μm. It was subjected to a surface smoothing treatment and a back coat, and then cut into 8 mm width to obtain a magnetic tape.

Polyurethane resin in Comparative Example 1 Example 1 (-SO ₃ Na, OH group-containing) a polyurethane resin containing no -SO ₃ Na in place of (O
A magnetic tape was obtained in the same manner as in Example 1 except that the H content was 0.03 wt% and Tg was 20 ° C.).

Polyurethane resin (-SO ₃ Na, OH group-containing) in Comparative Example 2 Example 1 in place of the polyurethane resin (manufactured by Toyobo Co., Byron UR8300) containing no -OH groups except for using the the same manner as in Example 1 To obtain a magnetic tape.

Comparative Example 3 Nipporan H manufactured by Nippon Polyurethane Co., Ltd. was used in place of the polyurethane resin (containing —SO ₃ Na, OH group) in Example 1.
A magnetic tape was obtained in the same manner as in Example 1 except that -2301 was used.

The magnetic tape obtained in Example 1 and Comparative Examples 1 to 3 was used.
C / N and still durability were measured using a VTR.

The C / N was determined by using a Sony VTR, EV-9000, recording a 7 MHz sine wave signal, inputting the reproduced signal to a spectrum analyzer, and comparing the signal intensity between 7 MHz and 6 MHz.

Still durability using VTR, EV-S9000, 5 ℃, 60% RH
After recording the signal under the conditions described above, the signal was reproduced in the still mode, and evaluated by the time required for the reproduced output to fall by 3 dB or less from the initial value.

 Table 1 shows the results.

[Effects of the Invention] As described above, when a fine metal magnetic powder having a BET specific surface area of 48 m ² / g or more is used as a high recording density magnetic recording medium, the SO ₃ of 1000 ppm or more in terms of S amount as a binder component is used. M, OH group-containing polyurethane resin and -SO ₃ M, or It is clear that a magnetic recording medium having excellent electromagnetic conversion characteristics and durability can be obtained by using a vinyl chloride resin containing at least one of the above and an -OH group.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-283775 (JP, A) JP-A-61-83272 (JP, A) JP-A-61-180927 (JP, A) JP-A 63-83927 263629 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C09D 5/23 C09D 175/04-175/12 C09D 127/06 G11B 5 / 702,5 / 714

Claims (1)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer on a non-magnetic support, wherein the magnetic layer has a BET specific surface area of at least 48 m ² / g, a fine metal magnetic powder, and a hydroxyl group and —SO ₃ M (M
Is a hydrogen or an alkali metal, a -SO ₃ M content of which is 1000 ppm or more in terms of S amount) as a functional group, a polyurethane resin and -SO ₃ M (M is hydrogen or an alkali metal), (R1, R2 are hydrogen or quaternary amine)
A magnetic recording medium comprising a seed and a vinyl chloride resin having a hydroxyl group as a functional group.