JPH0581647A - Magnetic coating material and magnetic recording medium - Google Patents

Abstract

PURPOSE:To solve such problems as the shaving of a coating film, variation of output and drop-out due to shavings and to provide a magnetic recording medium having excellent durability while maintaining high electromagnetic transducing characteristics by preparing a novel magnetic coating material. CONSTITUTION:The total amt. of free fatty acid and free fatty acid ester in a magnetic coating material contg. ferromagnetic metal powder, an abrasive material. carbon black, a binder, fatty acid, fatty acid ester, etc., in a solvent is regulated to 0.5-2.0wt.% of the amt. of the magnetic powder. A hardening agent is added to the magnetic coating material and a magnetic layer is formed by coating with the coating material. The total amt. of fatty acid and fatty acid ester leached in THF from the magnetic layer of the resulting magnetic recording medium is regulated to 0.2-1.0wt.% of the amt. of the magnetic layer.

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 tape using a ferromagnetic metal powder (hereinafter, simply referred to as magnetic powder) as a magnetic powder, a magnetic coating material such as a magnetic disk, and a magnetic recording medium.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is formed by coating a magnetic coating material containing magnetic powder and a binder on a non-magnetic support made of polyethylene terephthalate (PET).
It is manufactured by drying.

In recent years, the demand for high density recording has increased,
In magnetic recording media such as magnetic tapes and magnetic discs used in video equipment, audio equipment, computers, etc., it is essential to realize a smaller recording wavelength and track width, and a thinner magnetic layer and support. There is. For this reason, magnetic powders having a large coercive force (Hc) and saturation magnetization (σs) and finer particles have been adopted as compared with the conventional oxide-based magnetic powders. Furthermore, the use environment of magnetic recording media is expected to become wider and harsher than ever due to the widespread use of magnetic recording / reproducing devices and the widespread use of built-in cameras, etc., further improving the durability of the magnetic layer. It is extremely important to do this.

To improve the electromagnetic conversion characteristics such as output in a high frequency range and C / N ratio as a countermeasure against these problems, the fine particles of the magnetic powder, the high packing, the high orientation, and the improvement of the surface property are taken. Is being considered. When the high-density recording, that is, the recording wavelength is shortened, the leakage magnetic flux from the minute magnet on the recorded medium does not reach far from the medium. Appears as a drop in. For this reason,
The surface of the tape for DAT, 8 mm VTR, high band 8 mm VTR, etc. is ultra-smooth. With such an ultra-smooth surface, it is inevitable that a space of several nanometers, which is determined by surface irregularities, can be maintained when the device is started or stopped. , In that case, an intermolecular force directly acts on the entire apparent contact surface. Since this action acts to increase the load, it sometimes causes unexpected and large damage, which easily causes scratches on the magnetic layer surface and causes magnetic powder to fall off the magnetic layer, resulting in drop. Problems such as out were more likely to occur.

In order to improve these durability, consideration is given to a binder resin in consideration of mechanical strength of a coating film, heat resistance, head abrasion resistance, adhesion to a base film, and the like.
Efforts have been made to increase the lubrication of the coating film surface (lower the friction coefficient). As the binder, generally, a thermoplastic or thermosetting resin is frequently used, and a vinyl chloride-vinyl acetate-vinyl alcohol copolymer having a molecular weight of tens of thousands or a polyurethane resin is used. Multiple types of resins are mixed and used. However, as magnetic powder with smaller particle size is used for high density recording, an appropriate amount of polar groups that are well adsorbed on the surface of the magnetic powder in the molecular chain is promoted in order to promote sufficient dispersion of the magnetic powder. A method of coordinating (JP-A-2-35621, etc.) and a method of specifying the mechanical strength and molecular weight of the binder (JP-A-60)
No. -11125) has been proposed. Also, as a measure for achieving high lubrication, use of a binder with a small surface tension, examination of the type and amount of higher fatty acid, addition of solid lubricant such as carbon, or use of a binder with high mechanical strength, etc. It was being appreciated. However, with these methods, the effect is limited, and there has been a problem that it is difficult to achieve both improvement in electromagnetic conversion characteristics toward higher density and running durability in the future.

[0006]

In order to improve the reproduction output and the C / N ratio in the high frequency region, the surface property is improved by making the magnetic powder finer and making it a highly dispersed coating and selecting a binder system. It is not so difficult to achieve, but it is not an exaggeration to say that the running durability in equipment such as a VTR is determined by how the friction coefficient can be reduced while maintaining this surface state. If the magnetic recording medium such as a magnetic tape has a high coefficient of friction, the magnetic layer may come into contact with the device system such as a magnetic head or a traveling post during running in a device such as a VTR, so that the magnetic tape magnetic layer may be formed in a short time. As a result, the coating film is scraped or the scraped powder adheres to the magnetic head, resulting in an increase in dropout (DO) and output fluctuation, or peeling of the magnetic layer and cutting of the tape. Also, the increase in the coefficient of friction is
In particular, it becomes a cause of shortening the life (still life) of the magnetic layer in the steel mode. Since these are remarkably accelerated under the use conditions of high temperature and high humidity or low temperature, it is an essential issue to secure running durability to realize the reduction of the friction coefficient of the surface smooth magnetic layer.

The present invention is to solve the above problems, and an object of the present invention is to provide a magnetic recording medium excellent in running durability as well as high output and high C / N ratio, and a magnetic coating material for realizing the same. And

[0008]

In order to achieve the above object, the present invention provides a magnetic paint containing a ferromagnetic metal powder (magnetic powder), an abrasive, carbon black, a binder and a fatty acid or a fatty acid ester in a solvent. The total amount of free fatty acid and free fatty acid ester is 0.5 to 2.0 with respect to the magnetic powder.
% of the magnetic paint, and a fatty acid and a fatty acid ester which are eluted from the magnetic layer to tetrahydrofuran (THF) of a magnetic recording medium which forms a magnetic layer by adding a curing agent to the magnetic paint and coating the hardener. It is an essential condition that the total amount of is 0.2 to 1.0 wt% with respect to the magnetic layer.

[0009]

According to the present invention, therefore, the amount of free lubricant in the magnetic coating film, which greatly affects the electromagnetic conversion characteristics and durability of the magnetic tape, is defined, and the amount of free lubricant in the dispersion-finished magnetic paint is controlled. As a result, high durability can be realized particularly in a state where high output and high C / N are maintained in a high frequency region. The specific operation will be described below.

As a method of promoting the lubrication effect on the surface of the magnetic layer, a) formation of a low surface energy layer, b) reduction of a contact area, c) formation of a solid lubrication layer, and d) formation of a surface layer having high mechanical strength Although formation may be considered, here, the release in the magnetic coating formed by controlling the amount of free fatty acids and fatty acid esters (not adsorbed to magnetic powder or other inorganic powder) in the magnetic paint is observed. It incorporates the low surface energy effect of controlling the amount of fatty acids and fatty acid esters (not bound by magnetic powder or other inorganic powders and binders).

Lubricants such as fatty acids and fatty acid esters are used by adding them after the dispersion of the magnetic powder and other inorganic powders has been completed in the usual paint preparation method. In order to exert a low surface energy effect, it is present in a free state without being adsorbed by magnetic powder or other inorganic powder as much as possible, and it is present in a coating film surface layer or open pores (Open Por) during coating film formation.
It must be designed so as to segregate to e) by the required amount. If the amount is too small, the lubricating effect will be halved, and if it is too large, blocking due to the protrusion of the lubricant (adhesion phenomenon between the magnetic layer and the base film) will occur. Therefore, the amount must be strictly controlled. is there.

Recently, in order to realize high output and high C / N, the magnetic powder has been further miniaturized. Since the surface energy of the magnetic powder increases corresponding to the specific surface area (BET), most of the magnetic powder is adsorbed by the magnetic powder even if a lubricant is added. The amount of free lubricant can be controlled without using a large amount of lubricant.

When the high BET magnetic powder is used as it is, a binder having a high adsorptivity and a high adsorption strength (eg, --COOH or --SO ₃ M, where M: H, K, Na, etc.) is previously adsorbed on the magnetic powder. The amount of free lubricant can be controlled by sufficiently blocking the adsorption points of the magnetic powder with a substance having a polar group (1). From the above, it is considered that the necessary amount of lubricant is present in the surface layer or open pores of the coating film due to the free lubricant which is not completely adsorbed by the magnetic powder in the paint. As a result, both the surface roughness of the magnetic coating film and the friction coefficient can be made compatible, and thereby high durability can be realized while maintaining excellent electromagnetic conversion characteristics.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording medium according to an embodiment of the present invention and a method for manufacturing the same will be described below with reference to the drawings.
In addition, all the parts of the component ratios in the examples are shown by parts by weight.

Example 1 Ferromagnetic metal powder as magnetic powder (average particle size: major axis = 0.17 μm, acicular ratio = 1)
0, coercive force = 127 kA / m, specific surface area = 50 m ² / g,
Using an adsorbed H ₂ O amount = 0.4%), an 8 mm video tape was prepared as an example sample of a magnetic recording medium by the following steps with the compounding ratios shown in (Table 1).

[0016]

[Table 1]

First, magnetic powder, carbon black, a mixed solvent (methyl ethyl ketone, toluene, cyclohexanone) and binders 1, 2, and 3 shown in (Table 2) were mixed in a planetary mixer (PLM), and then the solvent was added. Then, it is diluted and subjected to primary dispersion by a sand mill (SM). Aluminum oxide is added to this, and secondary dispersion by SM is further performed. Next, add lubricant and hardener, and add 0.4μ
After passing through the m filter, it is applied on a polyester film (PET) with a thickness of 10 μm, magnetic field orientation, drying, surface treatment of the magnetic layer with a super calender (surface treatment machine), etc., followed by thermosetting treatment. .. Further, a back coat layer containing carbon black as a main component was applied onto PET on the side opposite to the magnetic layer, and then cut into 8 mm width to obtain an 8 mm video tape.

[0018]

[Table 2]

(Examples 2 and 3) The lubricants (C18 and C18-C4) shown in (Table 3) were prepared at the ratios shown in the table by the same manufacturing process and composition (excluding lubricant) as in Example 1. 8 mm video tape was prepared by adding.

[0020]

[Table 3]

(Comparative Examples 1 and 2) The lubricants (C18 and C18-C4) shown in (Table 3) were prepared at the ratios shown in the table by the same manufacturing process and composition (excluding lubricant) as in Example 1. An 8 mm video tape of a comparative example sample was prepared by adding.

(Examples 4, 5 and 6) Ferromagnetic metal powder (average particle size: major axis = 0.17 μm, acicular ratio = 9, coercive force =) was used as magnetic powder by the same manufacturing process as in Example 1. 1
26 kA / m, specific surface area = 58 m ² / g, adsorbed H ₂ O amount =
0.4%) and the binders 1, 2 shown in (Table 2),
4 and the lubricants (C18 and C1) shown in (Table 3).
8-C4) was added at the ratio shown in the table to prepare an 8 mm video tape.

(Comparative Examples 3 and 4) The lubricants (C18 and C18-C4) shown in (Table 3) were prepared in the proportions shown in the table by the same manufacturing process and composition (excluding lubricant) as in Example 4. 8 mm video tape was prepared by adding.

(Examples 7, 8 and 9) The lubricants (C14, C18, C22 and C18-C) shown in (Table 3) were prepared by the same manufacturing process and composition (excluding lubricant) as in Example 4.
4) was added at the ratio shown in the table to prepare an 8 mm video tape.

The characteristics of each sample described above (Table 4),
(Table 5) and FIG. 1 collectively.

[0026]

[Table 4]

[0027]

[Table 5]

The evaluation method will be described below. (1) Adsorption amount of binder to magnetic powder In a 50 ml polyethylene container, 2 g of magnetic powder and a mixed solvent (methyl ethyl ketone: toluene: cyclohexanone =
1: 1: 1) 20 g and 1 mmφsus beads 30 g were added, and this was shaken with a paint shaker for 30 minutes,
The supernatant is separated with a centrifuge (2 × 10 4 rpm for 1 hour). After 10 mL of this supernatant liquid was evaporated to dryness on a hot plate, the weight was measured to determine the non-adsorbed amount, and the difference from the total binder amount contained in the magnetic paint was calculated, and this was taken as the adsorbed amount.

(2) Amount of free lubricant in the paint A mixed solvent was added to the paint after addition of the lubricant to prepare a solid content concentration of 10%, which was then centrifuged (2 × 10 4 rp).
m) for 1 hour). This supernatant liquid 10
After evaporating and drying ml on a hot plate, the weight is measured. Then, the solution obtained by adding THF to the evaporated dry matter and dissolving it is GP
It is analyzed by C (gel permeation chromatography), and the amount of free lubricant is determined from this.

(3) Amount of lubricant extracted from magnetic coating film (amount of free lubricant in coating film) 2m of 1/2 "tape from which C layer was peeled off and 20 ml of THF were added, and this was added to 20 to 2
Ultrasonic vibration is applied for 30 minutes at 5 ° C. After removing the tape, 10 ml of this supernatant liquid was evaporated to dryness on a hot plate, and the weight was measured. And T to evaporate
The solution in which HF was added and dissolved was analyzed by GPC, and the amount of extracted lubricant was obtained from this.

(4) Dynamic friction coefficient According to the drawing formula, at 23 ° C-60% RH atmosphere,
The value of the 20th pass (μ
K20) was calculated.

(5) Surface Roughness The root mean square roughness (Rrms: nm) of the magnetic layer surface of each 8 mm VTR video tape was measured using a stylus type surface roughness meter (Taristep: made by Taylor Hopson). ..

(6) C / N (5 MHz / 4.5 MHz) The ratio of the signal at 5 MHz and the noise at 4.5 MHz is calculated by measuring an 8 mm video tape recorder (MV for measuring C / N).
S-5000: manufactured by KODAK Corporation. An amorphous alloy was used for the recording / reproducing head, and the relative value was shown with the C / N of a commercially available 8 mm video tape as a reference (0 dB).

(7) Still life Using an 8 mm video tape recorder modified for still measurement, a still image previously recorded under the condition of a load of 30 g is reproduced in an environment of -10 ° C, and the image signal is 3d.
The time (minutes) until B fell was shown.

(8) Dropout Using an 8 mm video tape recorder similar to that for C / N measurement, 16 dB or more in 15 μs per minute before and after running a video tape sample for 200 passes in an environment of 40 ° C./80% RH. The number of occurrences of the decrease in output (fixed number / minute) was measured and indicated by the multiple of increase from the initial value.

From Tables 4 and 5 and FIG. 1, the amount of free lubricant in the paint is 0.5 to 2.0 wt%, and the amount of free lubricant in the coating film is 0.2 to 1. About 0 wt%, good running durability was obtained while maintaining a high C / N ratio. However, for those outside the range, C
This resulted in inconvenience in the / N ratio and durability.

[0037]

Although the example of the 8 mm video tape has been described above, the present invention is suitable for high density recording and high durability, and can be applied to commercial and consumer video tapes, digital audio tapes and the like. It is applicable.

As is apparent from the above-mentioned embodiment, the present invention is
Ferromagnetic metal powder, abrasive, carbon black,
A magnetic coating material in which the total amount of free fatty acid and free fatty acid ester in a magnetic coating material containing a binder and fatty acids, fatty acid esters, etc. is 0.5 to 2.0 wt% with respect to the magnetic powder, and the above magnetic coating material is cured. A magnetic recording medium having a magnetic layer formed by adding the agent to the magnetic layer, wherein the total amount of fatty acid and fatty acid ester eluted from the magnetic layer into tetrahydrofuran (THF) is 0.2
Since it is a magnetic recording medium of about 1.0 wt%, good running durability can be secured while maintaining high electromagnetic conversion characteristics.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the amount of free lubricant from a magnetic coating film of a magnetic recording medium and durability in one example of the present invention.

Claims (2)

[Claims] 1. A magnetic paint containing a ferromagnetic metal powder, an abrasive, carbon black, a binder and a fatty acid or a fatty acid ester in a solvent, wherein the total amount of free fatty acid and free fatty acid ester in the magnetic paint is A magnetic coating material which is 0.5 to 2.0 wt% with respect to the ferromagnetic metal powder. 2. A magnetic recording medium having a magnetic layer formed by adding a curing agent to the magnetic paint according to claim 1 and coating the hardener, wherein the fatty acid is eluted from the magnetic layer in tetrahydrofuran (THF). And a fatty acid ester in a total amount of 0.2 to 1.0 wt% with respect to the magnetic layer.