JPH04324115A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics, slidability and durability by using a magnetic coating liquid contg. ferromagnetic powder having a specific surface area, alumina having a specific average grain size, and >=2 kinds among 4 kinds of specific compds. at specific component ratios. CONSTITUTION:A magnetic layer is formed on a nonmagnetic base by using the magnetic coating liquid contg. the ferromagnetic powder having >=300m<2>/g specific area by a BET method, the alumina powder having 0.1 to 1.5mum average grain size which is <=1.2 times the film thickness of the magnetic layer, and >=2 kinds of the compds. among aliphat. alkyrol amide compd., sorbitan esterification compd., org. boron compd. of the structure expressed by formula I, and org. boron double compd. at 25 to 120 pts.wt. per 100 pts.wt. of this alumina powder. The magnetic recording medium having the improved electromagnetic conversion characteristics, slidability and durability is then 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, and more particularly to a high-density magnetic recording medium having particularly excellent electromagnetic characteristics, slipperiness, and durability.

0002

[Prior Art] In recent years, in order to increase the recording density of magnetic recording media, especially video tapes and floppy disks, magnetic powders such as Co-containing γ-Fe2O3, barium ferrite, iron, and alloys with small particle sizes and large specific surface areas have been used. Magnetic powders such as these have come to be used. but,
These magnetic powders are extremely difficult to disperse and tend to cause agglomerated particles, insufficient filling, and non-uniform coating surfaces, which impair the electromagnetic properties of the coating (magnetic layer). It has the disadvantage that it tends to cause a decrease in slipperiness and durability.

[0003] In addition, recently, efforts have been made to increase the recording capacity and miniaturize devices, which has improved electromagnetic conversion characteristics at low recording wavelengths, and enables stable long-term operation even with small, low-capacity drive motors. As such, requirements regarding slipperiness and durability are becoming increasingly strict.

[0004] In order to improve sliding properties and durability, non-magnetic inorganic powders have traditionally been incorporated into magnetic layers. When the particle size is small, the effect is small, and as the particle size becomes larger, the effect of reducing the coefficient of friction tends to increase. If the particle size is made too large, the smoothness of the magnetic layer surface will be impaired.
Decrease electromagnetic conversion characteristics. Furthermore, if the particle size is large enough to reduce the friction coefficient sufficiently, the wear resistance will actually decrease.
There are other difficulties.

[0005] In order to improve these drawbacks of inorganic powders, attempts have been made to surface-treat the powders with surfactants having fatty acids or lipophilic groups, but as mentioned above, the required performance has become more sophisticated. At present, no material with satisfactory characteristics has yet been obtained.

[0006]

[Problem to be Solved by the Invention] The purpose of the present invention is to
The object of the present invention is to provide a new magnetic recording medium for high recording density. Second, the specific surface area according to the BET method is 30 g/m2
By using the above-mentioned ferromagnetic powder and coexisting a large amount of a specific surfactant with the alumina powder added as a reinforcing agent, the dispersibility in the coating liquid and the adhesion with the binder are improved. An object of the present invention is to provide a magnetic recording medium for high recording density that has well-balanced improvements in properties, slipperiness, and durability.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention consists of the following configuration.

[0008] In a magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating liquid containing ferromagnetic powder and a binder on a non-magnetic substrate, the ferromagnetic powder has a specific surface area of 30 m2 /g by the BET method. 100 parts by weight of the alumina powder, which is the above ferromagnetic powder, and the magnetic coating liquid has an average particle size of 0.1 to 1.5 μm and 1.2 times or less the thickness of the magnetic layer. 25 to 120 parts by weight of the following (1) to (4) (1) aliphatic alkylolamide compound (2) sorbitan ester compound (3) organoboron compound represented by the following structural formula.

0009
]

(4) A magnetic recording medium characterized by containing two or more compounds selected from four types of organic boron-based composite compounds.

The ferromagnetic powder used in the present invention is a ferromagnetic powder having a specific surface area of 30 m2/g or more, and the ferromagnetic powder includes conventionally known Co-containing γ-Fe2 O3,
Examples include oxide-based magnetic powders such as Co-containing Fe3O4 and barium ferrite, and metal-based magnetic powders such as iron and Fe-Co-Ni. Specific surface area is 30m
If it is less than 2/g, the purpose of high recording density cannot be achieved.

Examples of binders used in the present invention include vinyl chloride resins, vinyl chloride-vinyl acetate resins, saturated polyester resins, epoxy resins, and polyurethane resins, which have hydroxyl groups and carboxylic acid groups in their polymer chains. Those containing a polar group such as a group, a sulfonic acid group, a phosphoric acid group, an amino group, etc. can be suitably used.

The alumina powder used in the present invention acts as an agent for improving the wear resistance and slipperiness of the magnetic layer, and its average particle size is 0.1 to 1.5 μm, which is 1.5 μm of the thickness of the magnetic layer.
It needs to be 2 times or less. This average particle size is 1.5μm
If it is larger or larger than 1.2 times the thickness of the magnetic layer, the electromagnetic conversion characteristics are likely to be impaired and the wear resistance of the medium is also reduced. On the other hand, if the average particle size is smaller than 0.1 μm, it is impossible to improve slipperiness, which is one of the original objectives. It is preferable that the alumina powder has a sharper particle size distribution. Examples of the alumina powder include γ-alumina, θ-alumina, α-alumina, etc., and examples of the particle shape include granules, spheres, and gourd shapes.

■ Used as a surfactant in the present invention
As the fatty acid alkylolamide compound, the following formula A,
B,C

[0014]

Compounds represented by the formula (wherein R is H or a methyl group) can be exemplified.

The compound represented by formula A is monoethanolamide or monoisopropanolamide, such as Amizole CME manufactured by Kawaken Fine Chemicals Co., Ltd.
(coconut oil fatty acid monoethanolamide), Amizole L
Examples include ME (lauric acid monoethanolamide), Amizole SME (stearic acid monoethanolamide), Amizole PLME (lauric acid monoisopropanolamide), and the like.

The compound represented by the formula B is diethanolamide, for example, Amizole CDE (coconut oil fatty acid diethanolamide) manufactured by Kawaken Fine Chemicals Co., Ltd.
, Amizole LDE (lauric acid diethanolamide)
, Amizole MDE (myristic acid diethanolamide), Amizole LMDE (lauric acid, myristic acid diethanolamide), Amizole SDE (stearic acid diethanolamide), Amizole ODE (oleic acid diethanolamide), and the like.

The compound represented by the above formula C is an ethylene oxide (E.O) compound that converts monoethanolamide into monoethanolamide. For example, Amizet 2C (coconut oil fatty acid monoethanolamide 2E.O. )
, Amizet 5C (coconut oil fatty acid monoethanolamide 5E.O), Aminex HO (beef tallow fatty acid monoethanolamide ethoxylate), and the like.

These may be used alone or in combination of two or more as component (2).

■ Used as a surfactant in the present invention
Examples of sorbitan ester compounds include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquiolate, sorbitan dioleate, sorbitan triolate, and polyoxyethylene (hereinafter referred to as POE).
Sorbitan monolaurate, POE sorbitan monopalmitate, POE sorbitan monostearate, POE
Examples include sorbitan monooleate, POE sorbitan dioleate, and POE sorbitan triolate. These may be used alone or in combination of two or more as component (2).

■ Used as a surfactant in the present invention
The organic boron compound has the following structural formula

[0021]

This is a compound represented by the following formula. In this formula, when R1 is H, the organoboron compound is a compound having one fatty acid ester, such as glycerol/glycerol laurate borate, glycerol/glycerol palmitate borate, glycerol/glycerol oleate borate, glycerol/glycerol polyoxy Examples include ethylene laurate borate, glycerol/glycerol polyoxyethylene isostearate borate, and glycerol/glycerol polyoxyethylene oleate borate. Also, R1

[0022]

In the case of [Image Omitted], the organoboron compound is a compound having two fatty acid esters, such as diglycerol oleate borate, diglycerol polyoxyethylene stearate borate, and the like. These may be used alone or in combination of two or more as component (2).

■ Used as a surfactant in the present invention
Examples of organic boron-based composite compounds include Toho Chemical Industries (
Boron-phosphorus composite type PE-220 (composite type of organic boron compound and phosphate ester) and boron-nitrogen composite type EN-110, which are manufactured by Co., Ltd. and are commercially available as dispant.
Examples include EN-120 and EN-130 (both are composite types of an organic boron compound and an amine compound containing a fatty acid). These may be used alone or in combination of two or more as component (2).

It is preferable to use 25 to 120 parts by weight, particularly 30 to 100 parts by weight of two or more compounds selected from the surfactant components (1) to (4) to 100 parts by weight of the alumina powder. If this amount is too small, the dispersion of the alumina powder in the magnetic layer and its adhesion to the binder will not be sufficient, while if it is too large, the plasticizing effect on the binder will be too large, which will actually reduce the durability of the magnetic layer, so it is preferable. do not have.

Conventionally known techniques for surface treatment of inorganic powder include adding fatty acids or lipophilic dispersants to 100 parts by weight of inorganic powder from 0.01 part by weight to at most 1 part by weight.
The treatment was carried out by adding 0 to 15 parts by weight. The mixed compound of components (1) to (4) in the present invention exhibits surprising effects when a much larger amount of 25 to 120 parts by weight is added than these.

The reason for this is not clear, but this mixed compound is present on the surface layer of the alumina powder and helps its dispersion, and a part of it is mixed with the binder component, so that it is not only alumina powder but also a magnetic powder with a high specific surface area. It is thought that this increases the adhesion between the binders. This is supported by the fact that alumina powder with a large average particle size has a remarkable effect on improving durability. In addition, it is thought that wear resistance is partly improved by increasing the compatibility between the binder and the lubricant and increasing the lasting effect of the lubricant.

[0027] The surfactant in the present invention, that is, a mixed compound of any two or more of the above-mentioned components 1 to 2, also
As mentioned above, it has a plasticizing effect on the binder, so
17 to 40% by weight based on 100% by weight of the binder
It is preferable that If this proportion is less than 17% by weight, the dispersion effect of the alumina powder and the adhesion effect to the binder will be small, while if it exceeds 40% by weight, the dispersion effect will reach saturation, plasticization will become noticeable, and the magnetic layer will become soft. This is not preferable because the durability deteriorates.

As a method for treating alumina powder with a surfactant mixture, for example, (1) a method of dissolving the surfactant mixture in a suitable organic solvent, adding alumina powder, and mixing and stirring; (2) a method of dissolving the surfactant mixture in a suitable organic solvent; A method in which a suitable binder solution and a surfactant mixture are added, mixed and stirred (3) A method in which a surfactant mixture is added to a magnetic coating liquid consisting of ferromagnetic powder, alumina powder and a binder solution, and mixed and stirred, etc. be able to.

The magnetic coating liquid in the present invention can be prepared by mixing the ferromagnetic powder, binder, alumina powder, and two or more surfactants with an organic solvent such as methyl ethyl ketone, methyl isobutyl ketone, toluene, cyclohexanone, tetrahydrofuran, etc. During the preparation, conventionally known additives such as a dispersant (for example, lecithin, etc.) and an antistatic agent (for example, carbon black, etc.) may be added. Further, it is preferable to prepare the alumina powder by treating the alumina powder in advance with a surfactant mixture and then mixing it with a ferromagnetic powder.

[0030] In the present invention, a plastic film is preferably mentioned as the nonmagnetic substrate. More preferred are polyethylene terephthalate polymer films and polyethylene naphthalate polymer films. Preferably, such a film is a biaxially oriented film.

[0031] The surface (one side or both sides) of such a nonmagnetic substrate
A conventionally known method can be used to apply the magnetic coating liquid to the surface. As a coating method, for example, air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, gravure coating, die coating, etc. can be used. The coating amount is as follows: The thickness of the coating film (magnetic layer) after drying and calendering is 0.3
A range of 6 μm is preferable. For the treatment after coating, conventionally known treatment can be used.

The magnetic recording medium of the present invention has excellent electromagnetic characteristics, slipperiness and durability, and is useful as, for example, high recording density magnetic tapes and floppy disks.

[0033]

[Examples] The present invention will be further explained below with reference to Examples. Note that "parts" in the examples mean parts by weight. Further, the characteristics of the magnetic recording medium (floppy disk) were measured by the following method.

1) Electromagnetic conversion characteristics Using the following drive for each medium, determine the 2F output and nozzle at the innermost circumference, and compare it with a standard disk using the same type of magnetic powder. AA: Excellent, A: Same level, B: Slightly inferior,
C: It was judged as inferior.・Things using Co iron oxide powder: 3.5 inch FDDYD-685C (1F: 125K) made by YE Data Co., Ltd.
Hz, 2F: 250KHz) ・Those using methyl powder: NEC 3.5 inch FD
D FD-1331 (1F: 312.5KHz, 2F
:625KHz)

2) Slip property Using a 3.5-inch FDD FD-1135 manufactured by NEC Corporation, the motor current during head unloading and the motor current during track 00 head loading were measured at normal rotation of 360 rpm. From the difference, the current value required for friction between the media and the head was determined. This was converted into torque, and then the friction coefficient (μk) was calculated. In addition, the measurement was performed at 25℃50
It was carried out at ~60% RH, and the head tension was 22 g.

3) Durability Commercially available 3.5-inch FDD FD1137 manufactured by NEC
C, the head was loaded onto the outer periphery of the media (track 00) at the normal rotation speed (360 rpm) and head tension, and continuous rotation was performed using the same drag.

Tests were conducted by placing the drive in a constant temperature bath that was operated in one cycle per day, while setting the following four temperature and humidity conditions as the atmosphere every 6 hours. 25℃50%R
H→52℃80%RH→25℃20%RH→5℃free

The surface of the coating film was visually observed at 12-hour pitches, and the durability was defined as the total number of rotations (number of passes) until peeling first occurred on either side of the coating film.

[0039] Subtracting the time for checking etc., 1 day =
It was converted into 500,000 passes. The results are expressed as an average of the number of passes (n=3) (10,000 passes).

[0040]

[Example 1] Alumina powder 100 with an average particle size of 0.4 μm
Amizole LDE manufactured by Kawaken Fine Chemicals Co., Ltd. (
Alumina powder was dispersed by adding 60 parts of a 50/50 mixture of lauric acid diethanolamide and sorbitan monolaurate and a cyclohexanone/toluene mixture containing a polyurethane resin and stirring the mixture.

[0041]

[Table 1] Co-γFe2 O3 (specific surface area 32 m2
/g) 100 copies
Binder (vinyl chloride/vinyl acetate copolymer with polar groups and polyurethane resin (
(Including those used for alumina treatment)
and crosslinking agent consisting of polyisocyanate) 30.8 parts Alumina (use the one subjected to the above dispersion treatment)
9.2 parts 50/50 mixture of lauric acid diethanolamide and sorbitan monolaurate
5.5 parts
Lubricant (mixture of butyl stearate and oleyl oleate) 3.0 parts Cyclohexanone/toluene mixed solvent
350 copies

A magnetic paint was prepared by mixing and dispersing the components of the above composition.

This was applied to a 75 μm polyethylene terephthalate film so that the coating thickness after drying and calendering was 1.0 μm.
It was coated on both sides to a thickness of μm. Next, dry
The surface of the magnetic layer was smoothed by calendering, heated and cured, and then punched into a disk with a diameter of 90 mm. After polishing, a floppy disk was produced by a known method.

Table 1 shows the characteristics of this floppy disk.

[0045]

[Example 2] Alumina powder 100 with an average particle size of 0.2 μm
Amizole ODE manufactured by Kawaken Fine Chemical Co., Ltd.
Adding 30 parts of a 60/40 mixture of (oleic acid diethanolamide) and Dispant EN-120 (organoboron-nitrogen composite compound) manufactured by Toho Chemical Industry Co., Ltd. to a cyclohexane solution containing a polyurethane resin, and mixing and stirring. Dispersion treatment of alumina powder was performed using the following methods.

[0046]

[Table 2] Metal powder (specific surface area 42m2/g)
100 parts binder (same as Example 1)
23.1
Part: Alumina (using the above dispersion treated material)
15.4 parts
Oleic acid diethanolamide and dispant EN-1
60/40 mixture of 20

4.6 parts lubricant (same as Example 1)

3.0 parts cyclohexanone
400 copies

004
7] The components of the above composition were mixed and dispersed to prepare a magnetic paint.

[0048] This was applied to a 62 μm polyethylene terephthalate film with a coating thickness of 2.5 μm after drying and calendering.
The film was coated on both sides to a thickness of .mu.m, and a 3.5-inch floppy disk was obtained in the same manner as in Example 1.

Table 1 shows the characteristics of this floppy disk.

[0050]

[Example 3] Alumina powder 100 with an average particle size of 0.7 μm
Part 4 contains a 60/40 mixture of glycerol/glycerol borate isostearate and sorbitan sesquiolate.
6 parts and a tetrahydrofuran/cyclohexanone mixed solution containing a polyurethane resin were added, and mixed stirring was performed to perform a dispersion treatment of the alumina powder.

[0051]

[Table 3] Metal powder (specific surface area 41m2/g)
100 parts binder (same as Example 1)
26.2
Part: Alumina (using the above dispersion treated material)
11.1 part
60/40 mixture of glycerol/glycerol borate isostearate and sorbitan sesquiolate 5.1 parts
Lubricant (same as Example 1)
3.0 parts Tetrahydrofuran/cyclohexanone mixed solvent 400 parts

[0052]
The components having the above composition were mixed and dispersed to form a magnetic coating material, and a 3.5-inch floppy disk was obtained in the same manner as in Example 2.

Table 1 shows the characteristics of this floppy disk.

[0054]

[Example 4] Alumina powder 100 with an average particle size of 0.5 μm
Emulbon T-80 (POE) manufactured by Toho Chemical Industry Co., Ltd.
glycerol borate) and Kawaken Fine Chemicals Co., Ltd.
Alumina powder was dispersed by adding 110 parts of a 70/30 mixture of Amizole CDE (coconut oil fatty acid diethanolamide) manufactured by Co., Ltd. and a tetrahydrofuran/cyclohexanone mixed solution containing a polyurethane resin, and mixing and stirring.

[0055]

[Table 4] Metal powder (specific surface area 41m2/g)
100 parts binder (same as Example 1)
23.8
Part Alumina powder (use the one that has undergone the above dispersion treatment) 6.8 parts P
70/30 mixture of OE glycerol borate and coconut oil fatty acid diethanolamide

5.1 part lubricant (same as Example 1)

3.0 parts Tetrahydrofuran/cyclohexanone mixed solvent 40
0 copies

[0056] The components having the above composition were mixed and dispersed to form a magnetic coating material, and a 3.5-inch floppy disk was obtained in the same manner as in Example 2.

Table 1 shows the characteristics of this floppy disk.

[0058]

[Example 5] Alumina powder 100 with an average particle size of 0.4 μm
Dispant PE-220 (manufactured by Toho Chemical Industry Co., Ltd.) is installed in the section.
Alumina powder was dispersed by adding 30 parts of a 70/30 mixture of an organic boron-phosphorus composite compound) and sorbitan monooleate and a tetrahydrofuran/cyclohexanone mixed solution containing a polyurethane resin, and mixing and stirring.

[0059]

[Table 5] Metal powder (specific surface area 53m2/g)
100 parts binder (same as Example 1)
26.2
parts alumina powder (use the above dispersion treated powder) 11.1 parts dispant PE-220 and sorbitan monooleate
70/30 mixture

5.1 part lubricant (same as Example 1)

3.0 parts Tetrahydrofuran/cyclohexanone mixed solvent
450 copies

[0060] The components having the above composition were mixed and dispersed to form a magnetic coating material, and a 3.5-inch floppy disk was obtained in the same manner as in Example 2.

Table 1 shows the characteristics of this floppy disk.

[0062]

[Example 6] Alumina powder was used without pretreatment, and the following composition components were mixed and dispersed to make a magnetic paint.
Thereafter, a 3.5-inch floppy disk was obtained in the same manner as in Example 2.

Table 1 shows the characteristics of this floppy disk.

[0064]

[Table 6] Metal powder (specific surface area 43m2/g)
100 parts binder (same as Example 1)
26.2
Part Alumina powder (average particle size 0.4μm)
11.1 part
60/4 of glycerol/glycerol borate isostearate and sorbitan sesquiolate
0 mixture 5.1 parts
Lubricant (same as Example 1)
3
．． 0 parts Tetrahydrofuran/cyclohexanone mixed solvent 400 parts

00
65]

[Comparative Example 1] Example 1 except that the alumina powder was not treated with the surfactant mixture in Example 1, and the magnetic paint did not contain them (the binder was increased accordingly to 36.3 parts). I obtained a floppy disk in the same way.

Table 1 shows the characteristics of this floppy disk.

[0067]

[Comparative Example 2] In Example 2, the amount of the 60/40 mixture of Amizole ODE and Dispant EN-120 was changed to
A floppy disk was obtained in the same manner as in Example 2, except that the binder was reduced to 2.3 parts and the binder was increased to 25.4 parts.

Table 1 shows the characteristics of this floppy disk.

[0069]

[Comparative Example 3] Example 3 except that the alumina powder was not treated with the surfactant mixture in Example 3, and the magnetic paint did not contain these (the binder was increased accordingly to 36.3 parts). I obtained a floppy disk in the same way.

Table 1 shows the characteristics of this floppy disk.

[0071]

[Comparative Example 4] A floppy disk was obtained in the same manner as in Example 4 except that the composition was changed as shown below.

Table 1 shows the characteristics of this floppy disk.

[0073]

[Table 7] Metal powder (specific surface area 41m2/g)
100 parts binder (same as Example 4)
21.8
Part Alumina powder (0.5μm)
11
．． 1 part glycerol - 60/40 mixture of glycerol porate isostearate and sorbitan sesquiolate 15.
Part 6 Lubricant (same as Example 4)

3.0 parts Tetrahydrofuran/cyclohexanone mixed solvent 400 parts

[0074]

[Table 8]

[0075]

Effects of the Invention The magnetic recording medium of the present invention has well-balanced electromagnetic conversion characteristics at high recording density, slipperiness, and durability, and exhibits particularly excellent durability.

Claims (3)

[Claims] 1. A magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating liquid containing ferromagnetic powder and a binder on a non-magnetic substrate, wherein the ferromagnetic powder has a specific surface area of 30 m2 as measured by the BET method. /g or more, and the magnetic coating liquid has an average particle size of 0.1 to 1.5 μm and 1.2 times or less the thickness of the magnetic layer, and the alumina powder 100 25 to 120 parts by weight of the following (1) to (4) (1) aliphatic alkylolamide compound (2) sorbitan ester compound (3) an organoboron compound represented by the following structural formula [Formula 1] ( 4) A magnetic recording medium characterized by containing two or more compounds selected from four types of organic boron-based composite compounds. 2. The total amount of two or more compounds selected from the four types of compounds is 17 to 100 parts by weight per 100 parts by weight of the binder.
The magnetic recording medium according to claim 1, wherein the amount is 40 parts by weight. 3. The magnetic coating liquid according to claim 1, wherein the magnetic coating liquid is prepared by treating alumina powder in advance with two or more compounds selected from the above four types of compounds and then mixing it with ferromagnetic powder. magnetic recording medium.