JPH1021533A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an interfacial roughness and to improve the surface property by keeping a pH of powder within a specified range at the time of forming a non-magnetic layer being a lower lamination of a magnetic recording medium by applying a coating liq. of a non- magnetic powder, a binder and a solvent on a flexible non-magnetic supporting body. SOLUTION: A powder having the pH within 4.0-10.0 is used as the non-magnetic powder for forming the non-magnetic layer being the lower lamination of the magnetic recording medium to obtain the magnetic recording medium good in surface property. The pH ratio of a ferromagnetic metal powder to the pH of the non-magnetic powder is kept to 0.9-1.5 to obtain the excellent surface property since the pH of the ferromagnetic metal powder in the magnetic layer laminated on the non-magnetic layer being the lower lamination has an influence on the surface property even at this case. A resin excellent in adhesion and wear resistance with the flexible non-magnetic supporting body is used as the binder, and a crosslinking agent having a functional group at its part and forming a three-dimensional hexagonal network in the non-magnetic layer being a lower lamination by reacting with the binder is used together, and after applying the material, the binder is crosslinked and cured. In this way, the three-dimensional hexagonal is formed, and the non-magnetic layer being a lower lamination is converted to the material rich in rigidity and the supporting body is made thin.

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 recording medium. In particular, the present invention relates to a magnetic recording medium suitable for high-density recording, having a smooth surface, high output at high frequencies, and excellent overwrite characteristics.

[0002]

2. Description of the Related Art In recent years, the density of magnetic recording media has been increasing.
The recording wavelength has also become shorter. In high-frequency recording on a coating type magnetic recording medium, problems of self-demagnetization loss at the time of recording and thickness loss at the time of reproduction are great. Therefore, it is necessary to make the magnetic layer thin. However, simply reducing the thickness of the magnetic layer deteriorates durability and surface properties. Therefore, a magnetic recording medium having a multilayer structure of a lower layer containing a non-magnetic powder and an upper layer containing a magnetic powder has been proposed (Japanese Patent Application Laid-Open (JP-A) No. 2002-131131). Sho 62-154225, 15
No. 9338).

[0003]

However, in manufacturing a magnetic recording medium having a multilayer structure, how to form a lower layer and an upper layer is a problem. That is, the simplest method of applying the lower layer, drying and then applying the upper layer is as follows:
It is not suitable for mass production because the process becomes complicated. Further, in this method, when the upper layer is thinned, drying is quickened, and there is also a problem that the surface property is deteriorated and the orientation treatment of the magnetic powder is hindered. Furthermore, when the upper layer is applied, the upper surface of the lower layer swells, and the interface between the two layers becomes rough, so that there is a problem that the electromagnetic conversion characteristics of the magnetic recording medium deteriorate and the surface properties deteriorate.
Deterioration of surface properties becomes a problem particularly as the thickness of the upper magnetic layer becomes thinner.

Accordingly, it is desirable to apply the upper layer while the lower layer is in a wet state. However, this method is more likely to cause roughening of the interface between the two layers than the above-described method of applying after drying, such as mixing at the interface. . In addition, when a ferromagnetic metal powder effective for high-density recording is used as the magnetic powder, it is very difficult to find an appropriate combination of the lower layer and the upper layer because the powder easily aggregates.

[0005] In recent years, miniaturization of recording devices has been promoted due to the spread of notebook personal computers and the like, and with this trend, further miniaturization of drives, magnetic disk cartridges and the like has been required. Therefore, the thickness of the flexible non-magnetic support of the magnetic disk tends to be limited. However, if the thickness of the flexible non-magnetic support is reduced, the rigidity becomes insufficient, and the head cannot rotate smoothly in a state of contact. Accordingly, an object of the present invention is to provide a magnetic recording medium having a multilayer structure with excellent surface properties. The present invention also provides
An object of the present invention is to provide a magnetic disk which can be smoothly rotated even when a thin flexible non-magnetic support having low rigidity is used.

[0006]

According to the present invention, the nonmagnetic powder having a pH of 7.0 to 10.0 is used as the nonmagnetic powder of the lower nonmagnetic layer to reduce the roughness of the interface and improve the surface properties. Can be improved. That is, in the magnetic recording medium according to the present invention, a lower nonmagnetic layer containing a nonmagnetic powder and a binder is provided on a flexible nonmagnetic support, and a magnetic layer containing a magnetic powder and a binder is provided thereon. In the magnetic recording medium, the pH of the non-magnetic powder of the lower non-magnetic layer is 7.0 to 10.
It is characterized by being 0.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in further detail. The lower non-magnetic layer of the magnetic recording medium according to the present invention comprises a coating liquid mainly comprising a non-magnetic powder, a binder and a solvent.
It is formed by coating on a flexible non-magnetic support. The thickness of the lower non-magnetic layer is usually 0.1 to 4.0 μm, preferably 0.1 to 4.0 μm.
3 to 2.0 μm. As the nonmagnetic powder, an inorganic substance such as a metal oxide, a metal carbonate, a metal sulfate, a metal nitride, and a metal carbide is used. For example, graphite, titanium oxide, α-iron oxide, α-alumina, silicon carbide, chromium oxide, cerium oxide, goethite, corundum, silicon nitride, silicon dioxide, tin oxide, magnesium oxide,
Zirconium oxide, calcium carbonate, calcium sulfate,
Barium sulfate, molybdenum disulfide, or the like is used. Of these, preferred are titanium dioxide, α-iron oxide,
α-alumina, barium sulfate, calcium carbonate and the like. In particular, it is preferable to use titanium dioxide or α-iron oxide.

[0008] The size of these non-magnetic powders is usually 0.1.
It is preferably from 0.01 to 0.2 μm, particularly preferably from 0.02 to 0.08 μm. The specific surface area is usually from 1 to 100 m ² / g, preferably from 10 to 70 m ² / g. DBP oil absorption is 5-100ml / 100g, especially 10-80ml
/ 100 g is preferred. The shape of the nonmagnetic powder is arbitrary, and for example, a needle-like, spherical, polyhedral, plate-like or the like is used. Also, to increase dispersibility,
The nonmagnetic powder is preferably surface-treated with alumina, silicon dioxide, titanium dioxide, zirconium oxide, tin oxide, antimony oxide, zinc oxide, or the like. Particularly preferred are non-magnetic powders surface-treated with alumina and / or silicon dioxide. Alumina and silica are preferably attached to the nonmagnetic powder so as to be 0.1 to 10% by weight.

According to the present invention, a magnetic recording medium having good surface properties can be obtained by using those nonmagnetic powders having a pH in the range of 7.0 to 10.0. Even when a non-magnetic powder within this pH range is used, the surface properties are affected by the pH of the ferromagnetic metal powder in the magnetic layer laminated on the lower non-magnetic layer, and the ferromagnetic metal with respect to the pH of the non-magnetic powder. Particularly excellent surface properties are obtained when the pH ratio of the powder is in the range of 0.9 to 1.5. In the present specification, the pH of nonmagnetic powder and ferromagnetic metal powder
Shall be measured according to 24 of JIS K 5101.

The binder is a resin having excellent adhesion and abrasion resistance to a flexible nonmagnetic support, having a glass transition point of -100 to 150 ° C. and a number average molecular weight of 1,000 to 15,
It is preferable to use one of about 0000. Preferred resins to be used as the binder include polyurethane, polyester, cellulose acetate butyrate, cellulose derivatives such as cellulose diacetate and nitrocellulose, vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinylidene chloride copolymers. And vinyl chloride resins such as vinyl chloride-acrylic copolymers, various synthetic rubbers such as styrene-butadiene copolymers, epoxy resins, and phenoxy resins. These resins are used in the non-magnetic layer.
It preferably accounts for 占 め る 50% by weight, especially 5 to 35% by weight. In a preferred embodiment of the present invention, a binder having a functional group is used as at least a part of the binder, and a crosslinking agent that reacts with the functional group is used in combination. This forms a three-dimensional network structure,
Since the lower non-magnetic layer becomes rich in rigidity, a thin non-magnetic support having a thickness of 40 μm or less can be used.

As the cross-linking agent, any one can be used as long as it can react with a binder to form a three-dimensional network structure in the lower non-magnetic layer. For example, isocyanurate or the like is used, and a polyisocyanate compound is preferable from the viewpoint of handleability and reactivity. As the polyisocyanate compound, it is preferable to use a compound having a relatively low molecular weight which has a large mechanical strength and forms a three-dimensional network structure with high rigidity. Examples of such a polyisocyanate compound include toluene diisocyanate, methylene bisphenyl isocyanate, isophorone diisocyanate, hexamethylene diisocyanate and an adduct thereof with an active hydrogen compound, for example, a compound obtained by adding 3 mol of toluene diisocyanate to 1 mol of trimethylolpropane. Like, the molecular weight per isocyanate group is 400 or less,
Particularly, a polyisocyanate of 300 or less is used. The crosslinking agent is preferably used in an amount of 20% by weight or more, particularly 20 to 60% by weight, based on the binder.

In addition, in addition to the above, auxiliary agents such as carbon black, a lubricant, and a dispersant, which are added to the coating liquid when forming the magnetic layer, are appropriately added to the coating liquid for forming the lower nonmagnetic layer. May be. Examples of the solvent include methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propanol and isopropanol, esters such as methyl acetate, ethyl acetate and butyl acetate, ethers such as diethyl ether and tetrahydrofuran, Aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic hydrocarbons such as n-hexane and cyclohexane are used.

Examples of the flexible non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, aramid, polycarbonate and the like. Conventional ones can be used. Preferably, polyethylene terephthalate or another polyester is used. In order to improve the adhesiveness with the lower non-magnetic layer, the surface of the flexible non-magnetic support is treated with a corona discharge treatment or a surface modifier such as an aqueous amine solution, trichloroacetic acid, or phenols in advance. Processing may be performed beforehand.

The upper magnetic layer is prepared by adding various conventional auxiliaries to a suitable solvent in addition to a magnetic powder, preferably a ferromagnetic metal powder, and a binder to form a uniform coating solution. It is formed by coating on the surface. The thickness of the upper magnetic layer is 0.
The thickness is preferably 5 μm or less. If the thickness is more than 5 μm, it is not suitable for high-density recording in terms of self-demagnetization loss and thickness loss. The preferred thickness of the magnetic layer is 0.1-0.5 μm.

As the ferromagnetic metal powder, Fe—Co, F
Conventional ones such as e-Ni and Fe-Co-Ni can be used. Average long axis length of ferromagnetic metal powder is 0.5 μm
The thickness is particularly preferably 0.3 μm or less. The needle-like axis ratio is preferably 12 or less in order to increase the density of the ferromagnetic metal powder in the magnetic layer and increase the recording density. Among these ferromagnetic metal powders, σs is 120 emu / g or more,
Coercive force (Hc) of 1600 Oe or more, specific surface area of 40 m
² / g or more is preferable.

As described above, the ratio of the pH of the ferromagnetic metal powder to the pH of the nonmagnetic powder is preferably 0.9 to 1.5, and by controlling the ratio of the pH of both to this range, it is particularly excellent. A magnetic recording medium having improved surface properties can be obtained. The magnetic layer preferably contains as much ferromagnetic metal powder as possible, as long as durability and other characteristics permit.If the content of ferromagnetic metal powder in the magnetic layer is small, the recording density should be increased. Can not.

As the binder, any of those described as the binder for the lower non-magnetic layer can be used. The content of the binder in the magnetic layer is preferably 2 to 50% by weight, particularly preferably 5 to 25% by weight. The same solvent as that used for preparing the coating solution for forming the lower nonmagnetic layer can be used as the solvent. The coating liquid for forming the upper magnetic layer is essentially a uniform composition obtained by adding the above-mentioned ferromagnetic metal powder and a binder to a solvent, but usually further includes various kinds of additives. Additives such as crosslinking agents, dispersants, abrasives, antistatic agents, lubricants and the like are added. The cross-linking agent is for cross-linking the binder to form a three-dimensional network structure in the magnetic layer, and any of those described as the cross-linking agent for the lower non-magnetic layer can be used. Crosslinking agent is 10 to binder
Preferably, it is used so as to be 50% by weight.

As the dispersant, those having a phosphate group such as polyether phosphate and polyoxyethylene alkylphenyl phosphate are preferably used. Examples of such a dispersant include phosphatidylcholine (lecithin), RE-610 (manufactured by Toho Chemical Co., Ltd.),
PW-36 (manufactured by Kusumoto Kasei) and the like. Further, in addition to those containing a phosphate ester group, capric acid,
Fatty acids having 12 to 18 carbon atoms, such as lauric acid, myristic acid, oleic acid, and linoleic acid, metal soaps composed of alkali metal or alkaline earth metal salts of the fatty acids, and lecithin may be used in combination. The dispersant is used in an amount of 0.1 to 1 in the magnetic layer.
It preferably accounts for 0% by weight, especially 1 to 5% by weight.

Examples of the abrasive include α-alumina,
β-alumina, γ-alumina, α-iron oxide, silicon nitride, boron nitride, titanium oxide, silicon dioxide, tin oxide, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, tungsten oxide, silicon carbide, Chromium oxide or the like is used. Representative examples include AKP-20, AKP-30, and AK manufactured by Sumitomo Chemical Co., Ltd.
P-50, HIT-50, HIT-100, Toda Kogyo TF-100, TF-120, TF-140, Ishihara Sangyo FT-1000, FT-2000, Titanium Kogyo STT-4D, STT- 30, STT-65C, S-1, G5, G7 manufactured by Nippon Chemical Industry Co., Ltd., and among them, those having relatively high hardness are preferable.

The abrasive is preferably fine particles having a number average particle size of 0.5 μm or less. Abrasive is 1-10% by weight of magnetic layer
Preferably. Examples of antistatic agents include carbon black, conductive metals and their compounds and oxides, natural surfactants such as saponins, nonionic surfactants such as alkylene oxides and glycerins, higher alkylamines, and quaternary ammonium salts. , Cationic surfactants such as pyridinium salts and other heterocyclic salts, anionic surfactants containing an acidic group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a sulfate group, and a phosphate group, amino acids, and aminosulfonic acids. And amphoteric surfactants such as sulfuric acid or phosphoric acid esters of amino alcohol.

As carbon black, acetylene black, channel black, furnace black, thermal black and the like can be used. A typical example is BLACKPEARLS200 manufactured by Cabot.
0, 1000, 900, 800, VULCAN XC-
72, Raven 8800 manufactured by Columbian Carbon Co.,
8000, 7000, Mitsubishi Chemical Corporation # 3750B, # 3
750, # 3250B, # 3250, # 950, # 85
0B, # 650B, # 45, # 40, # 5, MA-7
7, MA-7 and the like. These carbon blacks may be surface-treated with a dispersant or the like, or may be partially graphitized.

As the conductive metal and its compound and oxide, tin oxide, tin-indium oxide and the like can be used. The antistatic agent is usually used to occupy 1 to 10% by weight of the magnetic layer. The antistatic agent may be used in expectation of its effect as a lubricant. Usually, fatty acid ester-based lubricants are used. Fatty acids may be monobasic or dibasic, and alcohols, even monohydric alcohols,
It may be divalent or trivalent. Further, the ester may be any of a monoester, a diester, a triester and the like. Examples of fatty acid esters include oleyl oleate, isocetyl stearate, dioleyl maleate,
Butyl stearate, butyl palmitate, octyl myristate, octyl palmitate, amyl stearate, isobutyl oleate, stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate, methyl oleate, isotridecyl oleate, 2-ethylhexyl palmitate, Methyl stearate, 2-
Ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, methyl laurate, cetyl-2-ethylhexanoate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate and the like.

The fatty acid ester lubricant is preferably used in an amount of 2 to 15% by weight, particularly 3 to 10% by weight, based on the ferromagnetic metal powder. If the amount is small, the durability of the magnetic recording medium becomes insufficient. In addition, the viscosity of the coating solution is high, and the dispersibility and workability may be poor. Conversely, if the amount is too large, the head may be contaminated. In addition to the fatty acid ester-based lubricant, fatty acids, fatty acid metal salts,
Fatty acid amides, aliphatic alcohols and the like may be used in combination.
As the fatty acid, for example, oleic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid and the like are used, and the amount used is 0.1 to
It is 10% by weight, preferably 1 to 5% by weight.

The upper magnetic layer is formed by a conventional method using a coating solution comprising the above-mentioned components. In the present invention, the upper magnetic layer is applied while the lower non-magnetic layer is in a wet state. As the coating device, any common device can be used. For example, it is possible to use a two-layer coating apparatus in which a discharge port for a coating liquid for forming a lower non-magnetic layer and a discharge port for a coating liquid for forming an upper magnetic layer are arranged in parallel. After the application, the magnetic recording medium is dried and cured according to a conventional method, and further subjected to calendering to obtain a magnetic recording medium. When a crosslinking agent is contained in either the upper layer or the lower layer, an appropriate temperature after calendering,
For example, the crosslinking is carried out while maintaining the temperature at 40 to 70 ° C. The magnetic recording medium according to the present invention basically comprises two layers, the lower layer and the upper layer. However, if desired, another auxiliary layer can be provided. For example, 3 having three application liquid discharge ports
An auxiliary recording layer can be formed between the upper and lower layers using a layer coating apparatus. Further, a lubricating layer may be further formed on the upper magnetic layer.

[0025]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. In the examples, "parts" represents parts by weight. Preparation of coating solution: The following compositions were used for the coating solution for forming the lower non-magnetic layer and the coating solution for forming the upper magnetic layer. The coating solution was prepared using a sand mill and filtered through a filter having an average pore diameter of 1 μm before use.

Coating solution for lower non-magnetic layer Non-magnetic powder ^{* 1} (α-Fe ₂ O ₃ , specific surface area 68 m ² / g) 30 parts Binder (polyester polyurethane) 10 parts Cross-linking agent (AD30 (product of Mitsubishi Chemical Corporation) Adduct of 3 moles of toluene diisocyanate and 1 mole of trimethylolpropane) 2 parts Methyl ethyl ketone 50 parts Cyclohexanone 50 parts ^{* 1 The} non-magnetic powder has been surface-treated. did.

Coating solution for upper magnetic layer Ferromagnetic metal powder (Fe / Co = 90/10, σs = 130 emu / g, Hc = 1800 Oe, specific surface area 58 m ² / g, pH = 9.3) 100 parts Binder ( Vinyl chloride copolymer) 10 parts Binder (polyester polyurethane) 10 parts Crosslinking agent (AD30 manufactured by Mitsubishi Chemical Corporation) 5 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts

Preparation of a magnetic recording medium: A coating solution for a lower non-magnetic layer was applied to a polyethylene terephthalate film having a thickness of 32 μm by an extrusion method so as to have a dry thickness of 0.7 μm. Immediately thereafter, a coating solution for an upper magnetic layer was applied thereon similarly by an extrusion method. After being dried with hot air, it was calendered at 100 ° C., and then cured at 60 ° C. for 72 hours. From this, a magnetic disk having a diameter of about 45 mm was cut out and the following measurement was performed. The results are shown in Table 1. The measured values are all average values for five magnetic disks.

Surface gloss: The sample before calendering was subjected to 60 ° using a BYK Gardner surface gloss meter.
Gloss and Haze were measured. In addition, Haze is the intensity of the reflected light deviated from the reflected light receiving unit having a gloss of 20 °. Surface roughness: Measured with a light interference type non-contact surface roughness meter (ZYGO). Output at 40 KftPi; measured by using a ferrite MIG head while rotating the disk at 500 rpm.

Overwrite erasure rate: 500 disks
Rotate at rpm and measure using ferrite MIG head. Measurement is 40K after recording / reproducing at 20KftPi
Superimposed recording / reproduction at ftPi, 20Kft before and after superimposed recording
The ratio of Pi output was defined as the overwrite erasure rate.

[0031]

[Table 1]

Claims (6)

[Claims] 1. A magnetic recording medium comprising: a lower non-magnetic layer containing a non-magnetic powder and a binder provided on a flexible non-magnetic support; and a magnetic layer containing a magnetic powder and a binder provided thereon. , The pH of the nonmagnetic powder in the lower nonmagnetic layer is 7.0 to 10.
0. A magnetic recording medium characterized by being 0. 2. The ratio of the pH of the ferromagnetic metal powder, which is the magnetic powder contained in the magnetic layer, to the pH of the nonmagnetic powder contained in the lower nonmagnetic layer is 0.9 to 1.5. The magnetic recording medium according to claim 1, wherein: 3. The ferromagnetic metal powder, which is a magnetic powder contained in the magnetic layer, has σs ≧ 120 emu / g and Hc ≧ 16.
3. The magnetic recording medium according to claim 1, wherein the specific surface area is 00 Oe and the specific surface area is ≧ 40 m ² / g. 4. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic layer is 0.5 μm or less. 5. The lower non-magnetic layer is formed by using a coating solution containing 20% by weight or more of a crosslinking agent with respect to a binder, and the thickness of the flexible non-magnetic support is 40 μm. 5. The magnetic recording medium according to claim 1, wherein: 6. A process of applying a coating solution for forming a lower non-magnetic layer on a flexible non-magnetic support, and applying a coating solution for forming a magnetic layer thereon while the coating solution is in a wet state. The magnetic recording medium according to any one of claims 1 to 5, wherein the magnetic recording medium is manufactured through the following steps.