JPH04178917A - Magnetic recording medium and its manufacturing method - 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 Industrial Application The present invention provides a ferromagnetic powder-coated magnetic material that has a magnetic layer with excellent surface smoothness, good electromagnetic conversion characteristics in the high frequency range, and excellent running durability. Related to recording media and their manufacturing methods.

2. Description of the Related Art In recent years, magnetic recording media in the form of magnetic tape have been widely used as information recording media in audio, video, and other fields. Recently, with the aim of achieving higher density recording, finer ferromagnetic powder has been developed using a type of vinyl polymer such as vinyl chloride copolymer containing a sulfonic acid group or its metal base in the molecule, and vinyl chloride-vinyl acetate copolymer. JP-A-59-5424 discloses high dispersion in an organic solvent containing a mixture of a polyurethane resin and a polyurethane resin. These binder resins introduce a highly hydrophilic functional group into the molecule in response to the fact that the primary particles of ferromagnetic powder have a strongly hydrophilic surface. This is intended to improve the dispersibility of ferromagnetic powder by adsorbing it to the site. If such a binder resin is used,
For example, even fine ferromagnetic powders with high coercive force (Hc) and strong magnetic cohesive force, such as metal magnetic powders, can be used in combination with recent advances in dispersion equipment and dispersion technology. Adsorption has been achieved and as a result a significant improvement in dispersibility has been observed.

Problems to be Solved by the Invention In such conventional magnetic paints, when the specific surface area (BET value) of the ferromagnetic powder increases, the adsorption of the binder resin to the surface of the ferromagnetic powder increases more than necessary. Then,
When this was coated on a non-magnetic support, oriented, dried, and subjected to calender surface smoothing treatment, the surface smoothness deteriorated.
The result was that high electromagnetic conversion characteristics could not be expected in the high frequency region. The reason for this is that if too much binder resin is adsorbed to the ferromagnetic powder, there will be less unadsorbed free binder resin that contributes to surface smoothing during calendering, and the amount of adsorbed binder resin will decrease. This is thought to be due to an increase in the apparent glass transition temperature (Tg). In order to achieve this condition, that is, to increase the amount of adsorbed resin and maintain excellent dispersibility while achieving excellent surface smoothness after calendering, the total amount of binder resin added must be increased. This can also be achieved by increasing non-adsorption bone. However, with this method, the packing density of the ferromagnetic powder in the magnetic layer decreases, and high electromagnetic conversion characteristics cannot be expected. Also, T
This can also be achieved by using a binder resin with a low g, but in this case there is a problem that the magnetic layer softens significantly in a high-temperature environment, resulting in poor high-temperature running durability.

The present invention solves this problem, and solves the problem of the conventional binder resin's excessive adsorption to ferromagnetic powder, which deteriorates the surface smoothness after calendering, by lowering the Tg of the binder resin. or eliminate the problem without increasing the amount added.
The object of the present invention is to provide a magnetic recording medium with good surface smoothness, excellent electromagnetic conversion characteristics, and high-temperature running durability.

Means for Solving the Problems In order to achieve this object, the present invention provides a magnetic layer which is provided on a non-magnetic support and whose main components are ferromagnetic powder and binder resin. It includes.

Furthermore, in the present invention, a solvent containing water is added to the ferromagnetic powder, the ferromagnetic powder is wetted and crushed, and then the ferromagnetic powder whose surface has been treated with an aluminum coupling agent is dispersed in an organic solvent containing a binder to form a magnetic paint. This is prepared by coating it on a non-magnetic support, orienting it, drying it, and subjecting it to a calender surface smoothing treatment.

In the present invention, water is first adsorbed onto the surface of the ferromagnetic powder, and then
Furthermore, an aluminum-based coupling agent is adsorbed. This surface treatment allows water to be adsorbed to the numerous adsorption sites present on the ferromagnetic powder surface, making the ferromagnetic powder surface more hydrophilic and facilitating the coupling reaction of the aluminum-based coupling agent to the ferromagnetic powder surface. Thus, strong chemisorption is efficiently achieved. As a result, the surface of the ferromagnetic powder becomes lipophilic, which makes it more compatible with the lipophilic portion of the binder resin, and it is thought that high dispersion is achieved. When measuring the adsorption amount of the binder resin per gram of magnetic powder in the magnetic paint obtained in this way, it was found that the adsorption amount of the binder resin per gram of magnetic powder in the magnetic paint obtained was smaller than that when no moisture and aluminum coupling agent were used. The amount is increasing. This increase in the amount of non-adsorbed resin improves the surface smoothness of the magnetic recording medium after calendering.

Examples Examples of the ferromagnetic powder used in the present invention include metal magnetic powder and iron oxide magnetic powder such as γ-Pe203 or Co-coated PezOz. For example, the average particle diameter is 0.25
Fine particle ferromagnetic powder that has a large specific surface area (for example, 45r+ (/g or more)) measured by the nitrogen adsorption method (μm or less) and is difficult to disperse is suitable. In the present invention, the water added to the ferromagnetic powder The purpose is to adsorb it to the surface of the powder, and for example, 0.5 to 3.0% by weight of the ferromagnetic powder is desirable.However, this addition range varies depending on the specific surface area of the ferromagnetic powder, and is not particularly limited. isn't it.

As a means of efficiently adsorbing water, it is common to use water added to one or a mixed solvent of methyl ethyl ketone, toluene, or cyclohexanone used in magnetic paints, but it is also possible to adsorb water alone. You can also add . Furthermore, the aluminum-based coupling agent used in the present invention is not particularly limited;
Conventionally known ones are used. For example, the product name AL-M of Ajinomoto Co., Inc. shown in formula (1) can be mentioned.

■ (R is H or an alkyl group) The amount of such aluminum-based coupling agent used is:
The amount is preferably in the range of 0.5 to 3.0% by weight based on the ferromagnetic powder adsorbed with water, but is not particularly limited.

Furthermore, according to the present invention, water is first adsorbed onto the ferromagnetic powder, and then an aluminum-based coupling agent is applied.

In this way, water will first be adsorbed to the numerous adsorption sites on the surface of the ferromagnetic powder, making the surface of the ferromagnetic powder more hydrophilic, promoting the coupling reaction of the aluminum coupling agent, and effectively making it stronger. Chemisorption is achieved. As a result, the surface of the ferromagnetic powder becomes lipophilic, which makes it more compatible with the lipophilic portion of the binder resin, and it is thought that high dispersion is achieved. When measuring the adsorption amount per gram of magnetic powder of the binder resin in the magnetic paint obtained in this way, the adsorption amount was smaller than when water and aluminum coupling agent were not used, and on the contrary, it was The amount of adsorption is increasing. It can be considered that this improves the surface smoothness after calendering.

As the binder resin used in the magnetic paint, conventionally known binder resins such as vinyl chloride-vinyl acetate copolymer and polyurethane resin can be used. Furthermore, the above magnetic paint may contain a lubricant, carbon black, abrasive, and a hardening agent, if necessary. The magnetic paint obtained as described above is applied to one side of a non-magnetic support, such as a polyethylene terephthalate film or a polyethylene naphthalate film, and subjected to orientation, drying, and calender surface smoothing treatment, and if necessary, the back side is coated. By providing a back coat layer on the magnetic layer, a magnetic recording medium with excellent surface smoothness of the magnetic layer and good electromagnetic conversion characteristics and running durability can be obtained.

Specific examples of the present invention will be shown and explained below.

Note that all parts indicating the amounts added below are parts by weight.

(Example 1) Mix magnetic paint with the following composition.

Ferromagnetic metal powder with homogeneous materials 100
Vinyl chloride-vinyl acetate copolymer... 1
0 parts polyurethane resin ・・・・・・
10 parts water ・
... 1 part aluminum coupling agent (A
L-M)... 1 part α-Ah(h
・・・・・・ 9 parts carbon black
・・・・・・ 1 part stearic acid
・・・・・・ Bipartite myristic acid
・・・・・・ 1 part n-butyl stearate
・・・・・・ 1 part ill (MEK/) toluene/cyclohexanone-3/2/1) ・・・・・・
235 parts The ferromagnetic metal powder used in the magnetic paint of this example is dry Fe powder with surface oxidation, and has a specific surface area:
56rrf/g, Hc: 15650e, a
s = 125 emu/g. The method for producing the magnetic paint having the above composition is as follows: First, ferromagnetic metal powder is mixed with MEK/l-luene/cyclohexanone-3/2/1 (weight ratio) 20
Add a mixed solvent of 1 part of water to 1 part of planetary
After kneading with a mixer and crushing the wet magnetic powder,
One part of an aluminum coupling agent (trade name AL-M) was added. After that, vinyl chloride-vinyl acetate copolymer (polymerization degree 330) and polyurethane resin (molecular weight MW 3
0,000) and various additives and continued kneading, and then dispersed magnetic powder using a sand mill to prepare a magnetic paint. After blending 20 parts of a polyisocyanate curing agent (trade name: Coronate Kago2 manufactured by Nippon Polyurethane) into the obtained magnetic paint, the mixture was mixed so that the thickness of the magnetic layer after calender surface smoothing treatment was 3.0 μm. Using a gravure roll, roll polyethylene terephthalate film (
After orientation treatment and drying, a back coat layer was provided, and the film was slit into a 2-inch width to prepare a videotape.

(Example 2) A videotape was produced in the same manner as in Example 1 except that the aluminum-based coupling agent in Example 1 was changed to 2 parts.

(Example 3) The Fe powder of the ferromagnetic metal powder of Example 1 was
rf/g, Hc: 1650.6 S = 1
A videotape was produced in the same manner as in Example 1, except that 35 emu/g of F powder was used and the water content was changed to 2.0 parts.

(Example 4) A videotape was produced in the same manner as in Example 3 except that the aluminum-based coupling agent in Example 3 was changed to 2.0 parts.

(Comparative Example 1) A videotape was produced in the same manner as in Example 1 except that the water in Example 1 was removed.

(Comparative Example 2) A videotape was produced in the same manner as in Example 1 except that the titanate coupling agent in Example 1 was omitted.

(Comparative Example 3) A videotape was produced in the same manner as in Example 3 except that the water and aluminum coupling agent in Example 3 were omitted.

The characteristics of the videotape obtained are shown in the table.

table The videotape evaluation method in the table is shown below.

(]) Adsorption amount: After diluting the solid concentration of the magnetic paint to 10%, the amount of free binder resin contained in the supernatant liquid is determined by centrifugal separation method and the difference from the total amount of binder resin added. It was calculated as

(2) Surface roughness: The center average roughness (Ra value) of the surface of the magnetic layer of the videotape was measured using a stylus type surface roughness system (Crystep, manufactured by Taylor Bobson).

(3) C/N (7MHz 15MHz): When recording and reproducing at a center frequency of 7MHz, the signal at 7MHz and 5M
The ratio of noise in Hz was measured. The C/N ratio is expressed as a relative value when Comparative Example 3 is set to OdB. For C/N measurement, an AU-650 VTR (manufactured by Matsushita Electric) was used.

(4) Output (10MHz) 1 recorded at a constant level
The output of 0 MHz was measured with a VTR (AU-650), and the relative value is shown when Comparative Example 3 is expressed as OdB.

(5) Powdered, dirty head: Use AU-650, 4
After reciprocating 20 times in an environment of 0°C and R880%,
Powder adhesion to the tape pad and magnetic head, and head stains were observed.

As a result, as shown in the table, all of the examples of the present invention exhibited superior characteristics compared to the comparative examples.

Effects of the Invention As is clear from the description of the embodiments above, the present invention provides a magnetic recording medium that has excellent surface smoothness after calendering, and has good electromagnetic conversion characteristics in the high frequency range and running durability. be able to.

Claims (2)

[Claims] (1) A magnetic recording medium in which a magnetic layer containing ferromagnetic powder and binder resin as main components, water and an aluminum-based coupling material is provided on a non-magnetic support. (2) A magnetic paint is prepared by adding an organic solvent containing water to ferromagnetic powder, and then dispersing the ferromagnetic powder, which has been coupled with an aluminum-based coupling agent, in an organic solvent containing binder resin; A method for producing a magnetic recording medium, which comprises applying the magnetic coating material onto a non-magnetic support, subjecting it to orientation treatment, drying it, and calendering the surface smoothing treatment.