JPH0540929A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability by incorporating an alternate copolymer consisting of the skeleton component of vinyl chloride and polyurethane introduced with sulfonic acid metal salt at the terminal into a magnetic coating material. CONSTITUTION:This magnetic recording medium is the magnetic recording medium formed with a magnetic layer consisting essentially of ferromagnetic metallic powder, vinyl chloride copolymer resin and polyurethane resin on a nonmagnetic base and is constituted by incorporating the alternate copolymer consisting of the skeleton component of the vinyl chloride and polyurethane introduced with the sulfonic acid metal salt at the terminal expressed by formula I into the above-mentioned magnetic layer. Then, the sulfonic acid metal salt introduced into the terminal of the alternate polymer is adsorbed and fixed to the surface of the ferromagnetic metallic powder. The surface of the magnetic layer is, therefore, improved and the excellent electromagnetic conversion characteristics are obtd. In addition, the magnetic recording medium having the excellent durability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a coating type magnetic tape or a magnetic disk which uses a ferromagnetic metal powder as a magnetic powder, and particularly to an electromagnetic conversion characteristic,
The present invention relates to a magnetic recording medium having excellent durability and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, the demand for high-density recording has increased, and magnetic recording media such as magnetic tapes and magnetic disks used in video, audio equipment, computers, etc.
It is becoming extremely important to realize smaller recording wavelengths and track widths and thinner magnetic layers and supports.

Therefore, both the coercive force (Hc) and the residual magnetic flux density (Br) of the magnetic layer can be increased, and a ferromagnetic metal powder suitable for improving the reproduction output in the short wavelength region has been adopted. However, the ferromagnetic metal powder has a larger saturation magnetization (σ _s ) than the conventional oxide-based magnetic powder and is finely divided for the purpose of achieving low noise. Easy to form structure,
As a result, the orientation of the magnetic powder becomes insufficient, and it becomes difficult to improve the filling properties of the magnetic powder in the magnetic layer as expected, and the surface properties and mechanical strength of the magnetic layer deteriorate, resulting in a high level. There was a problem that it was difficult to obtain the electromagnetic conversion characteristics and durability of.

Therefore, in order to improve the dispersibility of the ferromagnetic metal powder, the binder contains --SO ₃ M, --OS.
A method of introducing a polar group such as O ₃ M, —COOM, —PO (OM) ₂ (wherein M is a hydrogen atom or an alkali metal) has been proposed (JP-A-61-158023 and JP-A-61-258023). 2-35621).

In order to improve the durability of the magnetic layer, a plurality of binders are used, the number average molecular weight (Mn) of the binders is specified, and a hard segment such as an aromatic ring is used as a skeleton component of the binder. Methods such as introducing many have been proposed.

[0006]

However, it is very difficult to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and durability by using the method which has been conventionally used, and various problems are caused. Has occurred.

For example, the concentration of polar groups to be introduced into the binder must be determined by sufficiently considering the specific surface area, shape, and saturation magnetization (σ _s ) of the ferromagnetic metal powder.

When the concentration of the polar group is excessively increased, the strong interaction between the polar groups causes the binder to gel, and the amount of the binder adsorbed on the surface of the magnetic powder decreases, so that the dispersibility of the magnetic powder is reduced. It gets worse. On the contrary, when the concentration of the polar group is too low, the amount of the binder adsorbed on the surface of the magnetic powder becomes small and the dispersibility of the magnetic powder deteriorates. Even when a binder with an appropriate concentration of polar groups is used, if the amount used is too large, the spacing loss between the magnetic tape and the head may be due to the presence of excess binder on the magnetic layer surface. Is increased, resulting in deterioration of electromagnetic conversion characteristics.

Further, even when it is considered that both the concentration and the amount of the polar group are appropriate, the magnetic powder tends to be finely divided to have a large specific surface area in order to improve the filling rate of the magnetic powder in the magnetic layer. Therefore, more binder than necessary for dispersion is adsorbed on the surface of the magnetic layer, and the amount of non-adsorbed binder that contributes to calendering is reduced. As a result, it becomes difficult to improve the surface properties of the magnetic layer.

When a plurality of binders are used in order to improve the durability of the magnetic layer, the compatibility of the combined binders is not taken into consideration in the paint by simply specifying the individual characteristics of the binders. In many cases, the phase separation of the binder occurs and the mechanical strength such as the toughness and flexibility of the coating film decreases, and the expected effects cannot be obtained in many cases.

The present invention solves the above-mentioned problems.
It is an object of the present invention to provide a magnetic recording medium excellent in electromagnetic conversion characteristics and durability and a manufacturing method thereof.

[0012]

In order to achieve the above object, the present invention applies a magnetic coating material containing a ferromagnetic metal powder, a vinyl chloride copolymer resin and a polyurethane resin as a component on a non-magnetic support. A magnetic layer is formed by drying, and the magnetic coating material contains an alternating copolymer composed of a vinyl chloride and polyurethane skeleton component into which a metal salt of a terminal sulfonic acid represented by the following (Chemical Formula 2) is introduced. It will be the configuration.

[0013]

[Chemical 2]

[0014]

Therefore, according to the present invention, the sulfonic acid metal salt introduced at the terminal of the alternating copolymer is strongly adsorbed and fixed on the surface of the ferromagnetic metal powder. As a result, not only is it effective in improving the dispersibility of the magnetic powder, but since it is possible to reduce the number of residual adsorption sites on the surface of the magnetic powder necessary for dispersing the magnetic powder, it is possible to reduce the amount of binder added. It is possible to secure a sufficient amount of non-adsorbing binder that contributes to calendering. Therefore, the surface properties of the magnetic layer are good, and excellent electromagnetic conversion characteristics can be obtained. Further, since the alternating copolymer according to the present invention is formed from the skeleton components of vinyl chloride and polyurethane, the interfacial tension between the binders which are incompatible with each other is reduced. Therefore, the mechanical strength of the binder such as toughness and flexibility can be sufficiently exhibited, and a magnetic recording medium having excellent durability can be obtained.

[0015]

Examples As the ferromagnetic metal powder used in the present invention, acicular metal powder such as Fe, Fe-Co, Fe-Co-Ni can be mentioned. Further, in consideration of weather resistance, prevention of burning during manufacturing, and the like, needle-shaped metal powder containing a trace amount of added metal such as Al, Cr, and Si may be used.

An embodiment of the present invention will be described in detail below. In addition, each part number of the materials described in the examples and comparative examples indicates the number of parts by weight when the weight of the ferromagnetic metal powder is 100 parts by weight.

Example 1 Ferromagnetic metal powder: 100 parts by weight (specific surface area 57 m ² / g saturation magnetization 121 emu / g
Coercive force 15600e Adsorbed water content 0.54 wt%) Vinyl chloride copolymer resin: 8 parts by weight (Zeon Corporation, MR-110 glass transition temperature 59 ° C) Polyurethane resin: 4 parts by weight (Toyo Spinning Co., Ltd., AM-97 glass transition temperature 32
C) Polyurethane resin: 4 parts by weight (Toyobo Co., Ltd., UR-8700 glass transition temperature -23 ° C) Alternating copolymer: 2 parts by weight (number average molecular weight (Mn): 10,000) Abrasive・ ・ ・ 7 parts by weight (Sumitomo Chemical Co., Ltd., AKP-50) Carbon black ・ ・ ・ 1 part by weight (Tokai Carbon Co., Ltd., # 3800) Lubricant ・ ・ ・ 4 parts by weight Stearic acid ・ ・-2 parts by weight myristic acid ... 1 part by weight stearic acid-n-butyl ... 1 part by weight Curing agent ... 4 parts by weight (Takeda Pharmaceutical Co., Ltd., E-31) Mixed solvent ... 300 parts by weight (MEK / toluene / cyclohexanone = 3/2 /
1) Of the above compositions, ferromagnetic metal powder and carbon black are put into a planetary mixer under a nitrogen atmosphere (O ₂ concentration of 2% or less), and first mixed solvent 1
After wetting with 0 part by weight, an alternating copolymer composed of vinyl chloride having a sulfonic acid metal salt introduced at the terminal and a skeleton component of polyurethane is added and kneading is carried out for 3 hours.

Next, a mixed binder solution of vinyl chloride copolymer resin and polyurethane resin is added and kneading is carried out for 12 hours. Further, 180 parts by weight of an abrasive and a mixed solvent were added and dispersed by a sand mill to prepare a magnetic coating stock solution. Then, 70 parts by weight of a lubricant, a curing agent and a mixed solvent were added and mixed and stirred by a dissolver to prepare a magnetic paint. Then, the coating material filtered with a filter having an average pore size of 0.4 μm (HT-40 manufactured by Nippon Roki Co., Ltd.) was
It was applied on polyethylene terephthalate (PET) with a thickness of 0 μm, and subjected to orientation, drying, and mirror finishing by a super calendar. After further curing treatment, a backcoat layer containing carbon black as a main component was provided on polyethylene terephthalate on the side opposite to the magnetic layer, and the obtained magnetic recording medium was slit into a width of 8 mm to produce a metal tape for 8 mm VTR. did.

Comparative Example 1 An 8 mm VTR metal tape was produced in the same manner as in (Example 1) except that the alternating copolymer was removed from the coating composition of (Example 1).

Comparative Example 2 Instead of the alternating copolymer in (Example 1),

[0021]

[Chemical 3]

8 mmV was applied in the same manner as in Example 1 except that 2 parts by weight of a monoalkoxy type titanium coupling agent (TTS manufactured by Nippon Soda Co., Ltd.) represented by
A metal tape for TR was produced.

Comparative Example 3 Instead of the alternating copolymer in (Example 1),

[0024]

[Chemical 4]

By the same method as in (Example 1) except that 2 parts by weight of the alkylsilane coupling agent (A-163, manufactured by Nippon Unicar Co., Ltd.) represented by
A metal tape for mmVTR was produced.

The following measurements were carried out on the respective 8 mm VTR metal tapes obtained in the above Examples and Comparative Examples.

(1) Surface Roughness A non-contact type three-dimensional surface roughness meter (TOPO-3 manufactured by WYKO).
The measurement was performed using D). At this time, as a method of displaying the surface roughness of the magnetic layer, RMS which is the square root of the value obtained by integrating the square of the deviation from the center line to the roughness curve in the section of the measurement length and averaging in that section was adopted. ..

(2) C / N (5.0 MHz / 4.5 MH
z) The ratio of the signal at 5.0 MHz and the noise at 4.5 MHz was measured. MVS as 8mm TR for C / N measurement
-5000 (manufactured by KODAK Corporation) was used. The recording / reproducing head uses an amorphous alloy (Comparative Example 1).
8mm VTR metal tape C / N is the standard (0d
The relative value is shown as B).

(3) Amount of powder adhering to head / cylinder section Using the same 8 mm VTR for C / N measurement, each video tape is run for 200 passes under the environment of 40 ° C.-80% RH (endurance test). After the durability test, the amount of powder adhering to the magnetic head and the cylinder was observed with a microscope, and the degree of the amount of powder adhering was evaluated in five levels. As an evaluation, the case where no powder adhesion was observed and there was no problem in practical use was set to 5, and the case where the amount of powder adhesion was large and there was a problem in practical use was set to 1.

(4) Still life Using an 8 mm VTR modified for still measurement, -10 ° C
In this environment, a still image was recorded in advance under a condition of a load of 30 g and a still image was reproduced, and the time until the image signal dropped by 6 dB was shown. The measurement was terminated at a maximum of 90 minutes.

Table 1 shows the evaluation results of 8 mm VTR metal tapes prepared from the magnetic recording media of Examples and Comparative Examples.

[0032]

[Table 1]

As is clear from (Table 1), (Example 1) shows that the metal salt of sulfonic acid introduced at the end of the alternating copolymer used was strongly adsorbed and fixed on the surface of the ferromagnetic metal powder, and thus magnetic property was obtained. Not only the dispersibility of the powder was improved, but also the amount of the non-adsorbing binder contributing to the calendering property could be sufficiently secured, so that the surface of the magnetic layer became smooth and C
/ N became a high value. Furthermore, regarding the durability, the interfacial tension between the binders, which are incompatible with each other, could be reduced, resulting in a small amount of powder adhered to the head / cylinder portion after the durability test and a long still life. ..

In Comparative Example 1, as compared with Example 1, the amount of the binder not adsorbed and fixed (the amount of the non-adsorbed binder) was insufficient, so that the calendering property was deteriorated, and as a result, the surface roughness of the magnetic layer was deteriorated. However, the C / N became low. Moreover, the compatibility between the binders was not improved, resulting in poor durability.

(Comparative Example 2) was obtained by adding a monoalkoxy type titanium coupling agent, and
Although the calendar property was improved to some extent (Example 1)
It is not enough compared to.

In Comparative Example 3, the addition of the alkylsilane coupling agent deteriorated the surface property of the magnetic phase and significantly lowered the C / N. In addition, the durability was also insufficient. Since the long chain of the organic functional group of the silane coupling agent is shorter than the main chain of the alternating copolymer used in (Example 1), the dispersibility of the magnetic powder and the compatibility between the binders are not improved. It seems to be due to that.

Although only the 8 mm VTR metal tape has been described in the above embodiment, the present invention can be similarly applied to other coating type magnetic tapes using ferromagnetic metal powder, magnetic recording media such as magnetic disks.

[0038]

EFFECTS OF THE INVENTION As is clear from the above-described examples, the present invention is based on the alternating copolymerization of the vinyl skeleton component of vinyl chloride / polyurethane, in which the metal salt of sulfonic acid shown in the chemical formula 2 is introduced into the magnetic paint. Since the combination is contained, it is possible to exert an excellent effect on electromagnetic conversion characteristics and durability.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic layer containing a ferromagnetic metal powder, a vinyl chloride-based copolymer resin and a polyurethane resin as main components is formed on a non-magnetic support, wherein the magnetic layer comprises: A magnetic recording medium characterized by containing an alternating copolymer composed of a skeleton component of vinyl chloride / polyurethane in which a sulfonic acid metal salt is introduced at the terminal represented by the chemical formula (1). [Chemical 1] 2. A magnetic recording medium comprising a non-magnetic support and a magnetic coating material containing a ferromagnetic metal powder, a vinyl chloride-based copolymer resin and a polyurethane resin as main components, and dried to form a magnetic layer. A magnetic recording medium, characterized in that the above magnetic coating material contains an alternating copolymer comprising a skeleton component of vinyl chloride and polyurethane, in which a sulfonic acid metal salt is introduced at the terminal represented by (Chemical Formula 1). Manufacturing method.