JP2839485B2 - Magnetic recording media - Google Patents

Description

Description of the Invention [Object of the Invention] (Industrial application field) The present invention relates to a magnetic recording medium, and more specifically, excellent in running property and durability without deteriorating magnetic properties and high density. The present invention relates to a magnetic recording medium suitable for recording. (Prior Art) Among magnetic recording media, there are audio, video and computer tapes, floppy disks, etc. In recent years, high-definition television VTRs have been used.
High-definition magnetic tapes are also being developed. Among the above magnetic recording media, computer tapes, floppy disks, and high-definition magnetic tapes are used under severe conditions (for example, the frequency of repeated use is extremely high, etc.) as compared with audio and video tapes. High reliability, that is, excellent running performance and durability are required. 2. Description of the Related Art Conventionally, in order to improve running properties and durability, a process has been performed which has an effect of improving lubricity of a medium surface and preventing electrification due to sliding friction. That is, by adding a large amount of conductive carbon (for example, 5 to 7 parts by weight with respect to 100 parts by weight of magnetic powder) and a lubricant to the magnetic layer of the medium, the running property and durability are improved. However, the addition of a large amount of carbon or a lubricant, particularly the addition of a large amount of carbon, is extremely inconvenient in terms of increasing the density of a magnetic recording medium. That is, in the case of a magnetic recording medium for high-density recording, high dispersibility of the magnetic powder in the magnetic layer is required.
As a result, there is a problem that the magnetic properties of the obtained medium are deteriorated. For this reason, methods for solving such a problem have been disclosed in, for example, JP-A-50-114206 and JP-A-54-19712. It is possible to apply a conductive treatment to the base of a magnetic recording medium without adding a conductive substance such as carbon to the magnetic layer, or to conduct a conductive treatment by adding an alkyl sulfate salt or anhydrous calcium chloride to the magnetic layer. This is a method of providing on a substrate. These substances impart conductivity to the magnetic layer by ionic conduction. However, all of these methods focus only on the point of preventing the medium from being charged, and have some effects under the conditions where the charging is performed.
For a medium that requires a high degree of durability due to severe use conditions, such as a floppy disk and a magnetic tape for high definition, there is a problem that a sufficient effect cannot be obtained even if the above method is applied. . Although the above method has a large antistatic effect as compared with the method, the method of adding an alkyl sulfate salt or the like to the magnetic layer to impart conductivity to the magnetic layer by ionic conduction is sufficient under low humidity. There is also a disadvantage that an antistatic effect cannot be obtained. Further, in a magnetic recording medium using a hexagonal magnetic powder having high insulating properties and suitable for high-density recording as compared with Co-containing γ-Fe ₂ O ₃ etc. Due to insufficient conductivity, sufficient durability cannot be obtained. In addition, when a substrate not subjected to a conductive treatment is used, there is a problem that a large amount of conductive carbon must be added to the magnetic layer. Therefore, in this case, the dispersibility of the magnetic powder is likely to be reduced, and the use of a large amount of carbon deteriorates the magnetic properties of the medium, and the meaning of using hexacrystalline magnetic powder suitable for high-density recording is diminished. Is not preferred. (Problems to be Solved by the Invention) The present invention solves the above-mentioned problems, and provides a magnetic recording medium which is excellent in running properties and durability without deteriorating magnetic characteristics and suitable for high-density recording. The purpose is to: [Constitution of the Invention] (Means and Actions for Solving the Problems) As a result of intensive studies to achieve the above object, the present inventors have obtained excellent durability and running properties without deteriorating magnetic properties. In order to obtain a magnetic recording medium, (1) the surface resistivity of the substrate should be 10 ⁸ Ω or less, and (2) 0.05 to 100 parts by weight of the magnetic powder used for the magnetic layer.
(3) The binder resin is contained in the magnetic powder in an amount of 10 to 30 parts by weight, and (4) The lubricant is contained in the magnetic layer. It was found that the four conditions were essential, and the present invention was completed. That is, the magnetic recording medium of the present invention is obtained by applying a magnetic layer mainly composed of a magnetic powder, a binder resin, and a lubricant on one or both surfaces of a substrate and a conductive treatment layer formed on one or both surfaces of the substrate. In the magnetic recording medium formed by the above, 0.05 to 0.4 parts by weight (preferably 0.075 to 0.3 parts by weight) of carbon is added to 100 parts by weight of the magnetic powder, and the binder resin is added to 100 parts by weight of the magnetic powder. 10 to 30
Parts by weight (preferably 14 to 25 parts by weight) and 1.5 to 8.0 parts by weight (preferably 1.6 to
6 parts by weight). First, in the present invention, examples of the substrate on which the conductive treatment layer is to be formed include various films and disks made of polyester, polyethylene terephthalate, polyimide, polyamide, aromatic polyester and the like. The conductive treatment layer formed on one or both surfaces of the above-described base is a first essential requirement of the present invention. That is, this conductive treatment layer has a surface resistivity of 10 ⁸ Ω or less, preferably 10 ⁶ Ω or less.
Ω or less. As a method of forming the conductive treatment layer, a metal such as Al, Cr, N
There is a method of providing a vapor deposition film of i, Cu, Co, etc. on the substrate, and a method of providing an electroless plating film using Cr, Ni, Cu, Co, etc. as a plating metal on the substrate. However, these methods have an excellent effect on antistatic, but focusing on durability, on the other hand, because of the metal film, the adhesion with the magnetic film is weak, and it is not suitable for harsh materials such as floppy disks. It turned out to be unsuitable. In order to achieve both the adhesion and the antistatic effect, it has been found that the best method is to apply a coating material in which conductive carbon is dispersed on a substrate. Moreover, this method is simple and economical. First, as a component of the paint with carbon dispersed,
Conductive carbon may be used, and the same carbon as that contained in the magnetic layer described later may be used. The binder and the curing agent may be the same as the magnetic paint described later, and the binder is preferably a curing agent or a material which can be cross-linked by heat and light. Further, the thickness of the carbon coating film is not particularly limited as long as the surface resistivity is obtained. For example, in the case of a carbon coating film, a suitable surface resistivity can be obtained by setting the film thickness to 0.3 to 0.5 μm. Next, a magnetic layer formed on the above-described conductive treatment layer will be described. The magnetic layer in the present invention is a magnetic powder, a binder resin,
Lubricants, carbon, various additives (hardeners, dispersants, etc.)
It is obtained by applying a magnetic paint made of such as on the conductive treatment layer. Thereafter, the magnetic recording medium is obtained by subjecting it to ordinary orientation, drying and smoothing processes. The second essential requirement of the present invention is that a magnetic layer composed of the above components contains 0.05 to 0.4 parts by weight of carbon (preferably having good conductivity) based on 100 parts by weight of magnetic powder. That is. When the content of the conductive carbon is less than 0.05 part by weight, the conductivity in the magnetic layer is not sufficient and a satisfactory antistatic effect is not obtained, and as a result, sufficient running property and durability are not obtained. . On the other hand, when the content exceeds 0.4 parts by weight, dispersibility of the magnetic powder is hindered and magnetic properties are deteriorated. Preferably, it is 0.075 to 0.3 parts by weight based on 100 parts by weight of the binder resin. As the conductive carbon to be used, for example, Ketjen Black EC (manufactured by Lion Akzo) Ketjen Black
EC-DJ600, Ketchen Black EC-DJ500, Conductex SC (manufactured by Columbia Carbon), Vulcan XC (manufactured by Cabot) and the like. Next, a third essential requirement of the present invention is that the magnetic layer contains a binder resin. In this case, the resin binder is contained in an amount of 10 to 30 parts by weight based on 100 parts by weight of the magnetic powder. When the content of the binder resin is less than 10 parts by weight, the bonding strength of the coating film becomes insufficient, and the durability is reduced. When the content is more than 30 parts by weight, the magnetic properties are deteriorated. More preferably, it is 14 to 25 parts by weight. As the binder resin used in the present invention, for example, urethane resin, vinyl chloride-vinyl acetate copolymer,
Acrylic ester resins, polyvinyl butyral resins, polyester resins and the like can be mentioned. Next, a fourth essential requirement of the present invention is that the magnetic layer contains a lubricant. In this case, the lubricant is preferably contained in an amount of 1.5 to 8.0 parts by weight based on 100 parts by weight of the magnetic powder. If the content of the lubricant is less than 1.5 parts by weight, sufficient running properties cannot be obtained, and if it exceeds 8.0 parts by weight, the durability at low temperatures is undesirably reduced. More preferably, it is 2.0 to 6.0 parts by weight. Examples of the lubricant include various fatty acids and fatty acid esters, and it is preferable to use the fatty acid and the fatty acid ester in combination. The fatty acid may be saturated or unsaturated, and includes, for example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and the like. The fatty acid ester may be saturated or unsaturated, and includes, for example, methyl stearate, ethyl stearate, butyl stearate, butyl myristate, butyl laurate, methyl oleate, butyl palmitate and the like. Further, as the magnetic powder in the present invention, various magnetic powders can be applied, and for example, hexagonal magnetic powder, CrO ₂ ferromagnetic powder, Co-treated γ ferrite and the like can be used.
Among them, hexagonal magnetic powder is suitable for high-density recording. As the hexagonal magnetic powder, for example, Co or Fe, N
i-containing Co alloy; MnBi alloy; MnAl alloy; hexagonal ferrite containing various rare earth (R) and Co alloys such as RCo ₅ , R ₂ Co ₁₇ ; Ba, Sr, Pb, Ca, etc .; Substitution type hexagonal ferrite in which part of Fe of hexagonal ferrite is substituted with at least one element selected from the group consisting of Co, Ti, Ni, Mn, Cu, Zn, In, Ga, Nb, Zr, V, and Al Can be given. Of these magnetic powders, substitutional hexagonal ferrite is suitable for use in the present invention. (Example) Example A hexagonal barium ferrite was used as a magnetic powder to manufacture a double-sided floppy disk used under the most severe conditions and required to have excellent durability, and its durability and running properties were evaluated. . First, a conductive paint to be applied to the substrate was prepared with the composition shown in Table 1. After applying a conductive paint having the above composition to both surfaces of a 75 μm-thick polyester substrate, a curing treatment was carried out at 40 ° C. for 48 hours to form a 0.5 μm-thick conductive treatment layer. When the surface resistivity of the substrate was measured, it was about 4 × 10 ⁴ Ω. Next, a magnetic paint to be applied on the conductive treatment layer was prepared with a composition shown in Table 2. The amounts of the conductive carbon and the lubricant were varied as shown in Table 3, and as Comparative Examples 1 to 3, magnetic paints in which the amounts were outside the range of the present invention were also prepared. A magnetic paint having the above composition was applied on the conductive treatment layer, calendered, and then cured at 60 ° C. for 48 hours to obtain an evaluation sample. In order to evaluate the durability, the obtained floppy disk was loaded into a floppy disk drive configured such that the heads were in contact with both sides of the medium, and the disk was rotated at a rotation speed of 300 rpm. Then, the number of passes when the C / N ratio decreased IdB was measured under the respective environments of 5 ° C, 25 ° C, and 50 ° C. In addition, in order to evaluate the running performance, the friction coefficient before the running performance test and after 3 million passes was measured at a temperature of 25 ° C. Hereinafter, those in which the contents of the conductive carbon and the lubricant were changed are shown in Table 3, and those in which the contents of the binder resin and the lubricant were changed are shown in Table 4. [Effects of the Invention] As described above, the magnetic recording medium of the present invention has excellent durability and running properties without deteriorating magnetic properties.
In particular, the present invention relates to a severe use condition such as a floppy disk, a computer tape, a high-definition magnetic tape, etc. 90%). In addition, the present invention is also useful for a magnetic recording medium using hexagonal ferrite, which has high insulating properties and is suitable for high-density recording, has sufficient conductivity, and as a result, exhibits excellent durability and running properties. It is.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Koichi Shibusawa               1 201-1 Funakoshi-cho, Yokosuka City               Toshiba Yokosuka Factory                (56) References JP-A-55-55431 (JP, A)

Claims (1)

(57) [Claims] In a magnetic recording medium formed by applying a magnetic layer mainly composed of a magnetic powder, a binder resin, and a lubricant to one or both surfaces of a conductive treatment layer formed on one or both surfaces of a substrate, the magnetic powder 100 0.05 to 0.4 parts by weight
Contains carbon parts by weight, binder resin is magnetic powder 10
A magnetic recording medium characterized by containing 10 to 30 parts by weight with respect to 0 parts by weight and 1.5 to 8.0 parts by weight of a lubricant with respect to 100 parts by weight of magnetic powder. 2. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder is a hexagonal ferrite powder.