JPH05258285A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce the coefft. of friction of a magnetic layer, to reduce jitter and to enhance running stability by incorporating fatty acid esters, alpha-alumina and carbon black as well as magnetic powder into the magnetic layer. CONSTITUTION:A fatty acid ester having <=28 deg.C m.p., a fatty acid ester having >=38 deg.C m.p., alpha-alumina having <=1mum average particle diameter and carbon black as well as magnetic powder are incorporated into a magnetic layer. The carbon black has <=100nm average particle diameter and >=15m<2>/g specific surface area and satisfies the relation of 5 < oil absorption.X/specific surface area < 10 when the amt. of the carbon black basing on the amt. of the magnetic powder is expressed by X (wt.%).

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,
More specifically, the present invention relates to a magnetic recording medium in which the magnetic layer has a small friction coefficient, a small jitter, and excellent running stability.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is prepared by coating a base material such as a polyester film with a magnetic coating composed of magnetic powder, a binder resin, an organic solvent and other necessary components and drying it. Excellent running stability is required. Therefore, the magnetic layer contains a lubricant such as higher alcohol, fatty acid, fatty acid ester or the like to reduce the friction coefficient, reduce the jitter, and improve the running stability. There is.

[0003]

However, with the reduction in size and weight of the magnetic recording / reproducing apparatus, the adoption of a small diameter cylinder for mounting a magnetic head increases the magnetic tape winding angle and the cylinder rotation speed. Due to this, the load applied to the magnetic tape becomes large, and the traveling system becomes complicated and the regulation force of the magnetic tape by the guide post becomes large, so that the jitter tends to increase, and the high-grade alcohol in the magnetic layer tends to increase. −
Jitter cannot be sufficiently reduced by a conventional method such as containing a lubricant such as a phenol, a fatty acid or a fatty acid ester. Therefore, as a result of various investigations, the present inventors have already found that in the magnetic layer together with the magnetic powder, α-alumina having an average particle diameter of 1 μm or less, a fatty acid ester having a melting point of 28 ° C. or less, and a melting point of 38 ° C. When the above fatty acid ester is contained, the coefficient of friction is reduced, the jitter is reduced,
It was found that the running stability could be improved, but it was also found that it was still insufficient.

[0004]

The present invention has been made as a result of various investigations in view of the present situation. In the magnetic layer, α-alumina having an average particle diameter of 1 μm or less and a melting point of 28 are included in the magnetic layer together with the magnetic powder. Fatty acid ester having a melting point of 38 ° C. or higher, and an average particle size of 100
Carbon black having a specific surface area of not more than nm and a specific surface area of not less than 15 m ² / g, where X weight% is the content of this carbon black with respect to the magnetic powder, 5 <oil absorption amount X / specific surface area <10 By containing carbon black satisfying the relationship of (1), the friction coefficient is sufficiently reduced, the jitter is further reduced, and the running stability is further improved.

According to this invention, since the α-alumina having an average particle diameter of 1 μm or less is contained in the magnetic layer, the surface of the magnetic layer becomes hard and the contact area at the time of contact with the cylinder or the like on which the magnetic head is mounted. Is smaller, the protrusions on the surface of the magnetic layer having a surface roughness of 5 to 6 nm are suppressed due to the protrusions of the cylinder surface having a center line average roughness Ra of 160 nm and a surface roughness of 160 nm. As a result, the coefficient of friction with respect to the cylinder or the like is reduced, and the jitter is reduced.

Further, since the fatty acid ester having a melting point of 28 ° C. or lower and the fatty acid ester having a melting point of 38 ° C. or higher are contained, frictional heat is generated at the contact portion due to sliding contact with a cylinder or the like, and the environment changes. However, by using the lubricants having different melting points together, the lubricating effects under different conditions are complemented with each other, and a sufficient lubricating effect is exhibited without being influenced by frictional heat or environmental changes.

Further, in the case of carbon black having an average particle size of 100 nm or less and a specific surface area of 15 m ² / g or more, when the content of the carbon black with respect to the magnetic powder is X% by weight, 5 < Oil absorption / X / specific surface area <10
Since the carbon black satisfying the relationship is contained, the lubricating effect of this type of carbon black acts more synergistically to further reduce the coefficient of friction with respect to the cylinder and the like, and further reduce the jitter. It

Therefore, the magnetic recording / reproducing apparatus is reduced in size and weight, and a small diameter cylinder for mounting a magnetic head is adopted.
The load applied to the magnetic tape increases due to an increase in the wrap angle of the magnetic tape and an increase in the number of cylinder revolutions, and the traveling system becomes complicated and the regulation force of the magnetic tape by the guide post increases. However, the friction coefficient at the time of contact with the guide post, the cylinder, etc. is sufficiently reduced, the jitter is sufficiently reduced, and the running stability is sufficiently improved. In particular, when the carbon black is contained, the friction coefficient and the sitter are further reduced, and the running stability is further improved.

The α-alumina used in the present invention hardens the surface of the magnetic layer sufficiently to make the contact area when it comes into contact with a cylinder, a guide post, etc., on which the magnetic head is mounted, to sufficiently reduce the surface of the cylinder. In order to sufficiently suppress the protrusion of the magnetic layer surface caused by the protrusion of the, and to reduce the coefficient of friction with respect to the cylinder etc. to reduce the jitter,
Those having an average particle diameter of 1 μm or less are preferably used. The amount used is preferably in the range of 4 to 15% by weight with respect to the magnetic powder, and if it is less than 4% by weight, the desired effect will not be exhibited. The scratches become large, causing practical problems.

The lubricant is a fatty acid ester having a melting point of 28 ° C. or lower such as butyl myristate, heptyl myristate, butyl palmitate, and n-butyl stearate, ethyl arachiate, ethyl heaconate, and ethyl behenate. When a fatty acid ester having a melting point of 38 ° C or higher, such as tetradecyl myristate, tetradecyl palmitate, pentadecyl palmitate, and tetradecyl stearate, is used in combination, and when these lubricants are used in combination, they will slide in contact with the cylinder, etc. Even if frictional heat is generated or the environment changes, by using lubricants with different melting points together, the lubrication effects under different conditions are compensated for each other, and it is not affected by frictional heat or environmental changes. The excellent lubricating effect is exhibited, and the friction coefficient is sufficiently reduced.

The blending ratios of the fatty acid ester having a melting point of 28 ° C. or lower and the fatty acid ester having a melting point of 38 ° C. or higher are such that the lubricating effects under different conditions are sufficiently compensated for each other. The following weight ratio of fatty acid ester to fatty acid ester having a melting point of 38 ° C. or higher is used.
It is preferably within the range of 80:20 to 20:80.
In addition, the amount used is the total amount of both fatty acid esters blended in the above-mentioned ratio, and it is preferable to use it within the range of 0.5 to 4% by weight with respect to the magnetic powder. If the effect is not exhibited and the amount is more than 4% by weight, the magnetic layer is adversely affected and the durability is deteriorated.

Further, the carbon black contained in the magnetic layer has an average particle size of 100 nm or less and a specific surface area of 1
It is 5 m ² / g or more, and when the content of this carbon black with respect to the magnetic powder is X% by weight, it is preferable that the relationship of 5 <oil absorption amount / X / specific surface area <10 is satisfied, When the average particle size is larger than 100 nm and the specific surface area is smaller than 15 m ² / g, the surface smoothness is deteriorated and the electromagnetic conversion characteristics are deteriorated. Further, the content of this type of carbon black is 0.5 <X when the content based on the magnetic powder is X% by weight.
It is preferable to set it within the range of <5. If it is less than 0.5% by weight, the friction coefficient and the jitter cannot be sufficiently reduced.
When it is more than 5% by weight, the dispersibility of carbon black is lowered, the surface smoothness is lowered, and electromagnetic conversion characteristics are lowered.

The average particle size of α-alumina having an average particle size of 1 μm or less, the fatty acid ester having a melting point of 28 ° C. or less, and the fatty acid ester having a melting point of 38 ° C. or more are used.
0 nm or less, a specific surface area of 15 m ² / g or more, and the content of the magnetic powder is X% by weight, carbon black satisfying the relationship of 5 <oil absorption amount / X / specific surface area <10 is added. In order to include it in the magnetic layer, these are mixed and dispersed with a magnetic powder, a binder resin, an organic solvent and other necessary components to prepare a magnetic paint, which is coated on a substrate and dried to form a magnetic layer. It may be formed.

The magnetic powder used for forming the magnetic layer includes γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder and Co.
Γ-Fe ₂ O ₃ powder containing, Fe ₃ O ₄ powder containing Co, C
rO ₂ powder, Fe powder, Fe with Al, Cr, Mn, S
Magnetic powders generally used in magnetic recording media, such as powders mainly containing Fe containing elements such as i and Zn, Co powders, Fe-Ni powders, and barium ferrite powders are widely included, and metal magnetic powders are used. In this case, a particularly preferable effect is obtained.

As the binder resin, vinyl chloride-
Generally used as a binder resin for magnetic recording media, such as vinyl acetate-based copolymers, fibrin-based resins, polyvinyl butyral-based resins, polyurethane-based resins, polyester-based resins, isocyanate compounds, and radiation-curable resins. Things are widely used.

As the organic solvent, commonly used organic solvents such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, ethyl acetate and toluene may be used alone or in admixture of two or more.

In the magnetic coating composition, various commonly used additives such as a dispersant, an abrasive and an antistatic agent may be optionally added and used.

[0018]

Next, examples of the present invention will be described. Example 1 100 parts by weight of α-Fe magnetic powder Eslek E (manufactured by Sekisui Chemical Co., Ltd .; vinyl chloride-vinyl acetate 12.5 〃 copolymer) UR8310 (manufactured by Nippon Polyurethane Industry Co., Ltd .; urethane resin) 7.4 〃 Coronet L (Japan Polyfunctional Industrial Co., Ltd .; trifunctional low content 5.1 〃 quantity isocyanate compound) Monarch 120 (Cabot Co .; carbon black 3〃, particle size 75nm, specific surface area 25m ² / g, oil absorption 72 cc / 100g, Oil absorption / specific surface area = 2.88, oil absorption / X / specific surface area = 8.64) Red iron oxide 2〃 α-alumina 8〃 Myristic acid 2〃 Zinc stearate 0.5〃 Stirrate-n-butyl (melting point 27.5 ℃) 0.5〃 Myristic acid Tetradecyl (melting point 39.5 ° C) 1.0 〃 cyclohexanone 330 〃 toluene 330 〃 This composition was mixed and dispersed to prepare a magnetic paint. Was coated on the surface of a polyester film having a thickness of 9.5 μm so that the dry thickness would be 2.6 μm, dried, and subjected to calendar treatment to form a magnetic layer.

Next, the following backcoat layer composition was mixed and dispersed in a ball mill for 96 hours to prepare a backcoat layer coating material, and this backcoat layer coating material was used to form the above-mentioned magnetic layer. On the back of the polyester film, the dry thickness
A back coat layer was formed by coating and drying so as to have a thickness of 0.7 μm. Then, it was cut into a predetermined width to form a magnetic tape.

Backcoat layer composition Nitrocellose (manufactured by Asahi Kasei; Celnova H1) 40 parts by weight N2309 (manufactured by Nippon Polyurethane Industry Co., Ltd .; urethane resin) 45 〃 Coronet L (manufactured by Nippon Polyurethane Industry Co., Ltd .; trifunctional) Low-molecular-weight 15-compound isocyanate compound) Cast 5H (Tokai Carbon Co., Ltd .; Carbon Black) 60 Raven MT-P beads (Colombia Carbon Co., Ltd .; Carbon 7.5) 〃 Black) Calcium carbonate 30 〃 Bengala 2.5 〃 Cyclohexanone 330 〃 Toluene 330 〃

Example 2 In the composition of the magnetic paint in Example 1, Monar
Asahi Thermal (made by Asahi Carbon Co., Ltd .; carbon black, particle size 90 nm, specific surface area 19 m ² /
g, oil absorption amount 26 cc / 100 g, oil absorption amount / specific surface area =
A magnetic tape was produced in the same manner as in Example 1 except that 4 parts by weight of 1.37 and oil absorption / X / specific surface area = 5.5) were used.

Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that the amount of α-alumina used in Example 1 was changed from 8 parts by weight to 6 parts by weight.

Example 4 A magnetic tape was prepared in the same manner as in Example 1 except that the amount of α-alumina used in Example 1 was changed from 8 parts by weight to 12 parts by weight.

Comparative Example 1 In the composition of the magnetic coating material of Example 1, Monar
Example 1 except that the amount of ch120 used was changed from 3 parts by weight to 1.5 parts by weight (oil absorption / X / specific surface area = 4.32).
A magnetic tape was made in the same manner as in.

Comparative Example 2 In the composition of the magnetic coating material of Example 1, Monar
Example 1 except that the amount of ch120 used was changed from 3 parts by weight to 4.5 parts by weight (oil absorption / X / specific surface area = 12.96).
A magnetic tape was made in the same manner as in.

Comparative Example 3 In the composition of the magnetic coating material of Example 2, the amount of Asahi Thermal used was changed from 4 parts by weight to 3 parts by weight (oil absorption.
A magnetic tape was produced in the same manner as in Example 2 except that X / specific surface area = 4.11).

Comparative Example 4 In the composition of the magnetic coating material of Example 1, Monar
Instead of ch120, HS-500 (manufactured by Asahi Carbon Co., Ltd .;
Carbon black, particle size 43nm, specific surface area 30m ²
/ G, oil absorption amount of 640 cc / 100 g, oil absorption amount / specific surface area = 21.3, oil absorption amount / X / specific surface area = 64), except that the same amount was used to prepare a magnetic tape.

Comparative Example 5 In the composition of the magnetic paint in Comparative Example 4, HS-50 was used.
A magnetic tape was produced in the same manner as in Comparative Example 4 except that the amount of 0 used was changed from 3 parts by weight to 1.0 part by weight (oil absorption · X / specific surface area = 21.3).

Comparative Example 6 Comparative Example 6 was repeated except that the amount of the n-butyl stearate used was changed from 0.5 parts by weight to 1.5 parts by weight, and tetradecyl myristate was omitted from the composition of the magnetic coating material in Example 1. A magnetic tape was made in the same manner.

Comparative Example 7 Example 1 was repeated except that the amount of tetradecyl myristate used in the composition of the magnetic coating material of Example 1 was changed from 1 part by weight to 1.5 parts by weight and -n-butyl stearate was omitted. A magnetic tape was made in the same manner.

The friction coefficient, jitter and RF output were measured for each magnetic tape obtained in each of the examples and comparative examples. Friction coefficient is 5 ℃, 50% RH, 25 ℃, 50% R
Under each condition of H, 80 ℃, 50% RH, diameter 2
67mm aluminum cylinder (centerline average roughness 160
nm) with a magnetic tape at an angle of 90 degrees so that the surface of the magnetic layer abuts, a load of 11.7 g is applied to one end, and the other end is pulled back and forth 20 times at a speed of 14.3 mm / sec. It was determined by the load. Also, the jitter is 5 ° C., 50% RH, 2
Under 5 ° C, 50% RH, 80 ° C, 50% RH, the magnetic tape is 8 mm video beam (SONY
It is loaded into the CCD-TR45) and the video signal is recorded / reproduced, the interval of the horizontal synchronizing signal of 15.75 KHz of the reproduced signal is read, and the maximum value of the deviation of the horizontal synchronizing signal for 1 second at that time is measured with the jitter meter. did. In addition, the RF output is
It was measured by Sony EV-S700. Table 1 below shows the results.

[0032]

[0033]

As is apparent from Table 1 above, the magnetic tapes obtained in the present invention (Examples 1 to 4) are superior to the magnetic tapes obtained in Comparative Examples 1 to 7, The friction coefficient is small, the jitter is small, and the RF output is high. From this, it is understood that the magnetic recording medium obtained by the present invention has a small friction coefficient, a small jitter, and excellent running stability.

Claims (2)

[Claims] 1. A magnetic layer, together with magnetic powder, α-alumina having an average particle size of 1 μm or less, a fatty acid ester having a melting point of 28 ° C. or less, a fatty acid ester having a melting point of 38 ° C. or more, and an average particle size of 100 nm. Below, specific surface area is 15m ²
/ G or more of carbon black, the carbon black satisfying the relationship of 5 <oil absorption amount / X / specific surface area <10 when the content of the carbon black with respect to the magnetic powder is X% by weight. And a magnetic recording medium characterized by containing 2. The magnetic powder is a metal magnetic powder.
Magnetic recording medium described