JPH0770045B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk, and more particularly to a disk-shaped flexible magnetic recording disk.

[Conventional technology]

Generally, a magnetic recording medium is manufactured by applying a magnetic coating material containing magnetic powder, a binder resin (binder) and the like onto a non-magnetic support and drying it.

The binder resin for such a magnetic recording medium is required to have appropriate flexibility and appropriate strength at both low and high temperatures, and must be capable of well dispersing the nonmagnetic powder such as the magnetic powder and the abrasive, and the conductivity imparting agent to be used. I have to. In order to meet such demands, the present applicant has already developed a polyurethane resin containing 10-1000 equivalent / 10 ⁶ g polymer or a metal sulfonate base (Japanese Patent Application No. 53-66459, Japanese Patent Application Laid-Open No. 54-5459). No. 157603).

[Problems to be solved by the invention]

One of the important performances required for such a magnetic recording medium, especially a flexible magnetic recording disk such as a floppy disk, is to reduce the starting torque under high temperature and high humidity (for example, 45 to 60 ° C, 80% RH). Is. Various means have been proposed as measures against this, but none have been found to be sufficiently satisfactory.

[Means for solving problems]

INDUSTRIAL APPLICABILITY In addition to the advantages of the polyurethane resin containing a metal sulfonate group described above, the present invention also has the advantages of lowering the starting torque under high temperature and high humidity, improving moisture (water) resistance, and improving durability. The present invention provides a medium, the gist of which is a magnetic recording medium in which a magnetic layer containing a magnetic powder, a binder and a lubricant is formed on a non-magnetic support. The main component is polyurethane resin contained per 1000 equivalent / 10 ⁶ g polymer,
Lubricants have 12 to 18 carbon atoms, branched fatty acid esters with a melting point of 10 ° C or less, and butyl cellosolve
A magnetic recording medium is characterized in that it contains an ester with a fatty acid of 12 to 18 and the content of the fatty acid of 12 to 18 carbon atoms in the lubricant is 5 to 50% by weight.

In the present invention, as the main component of the binder of the magnetic powder, a polyurethane resin containing 10 to 1000 equivalents / 10 ⁶ g of the sulfonic acid metal base per polymer is used, but the sulfonic acid metal base per polymer is 10 equivalents. If it is less than / 10 ⁶ g, not only an increase in Br / Bm value cannot be expected, but also high packing property of magnetic particles cannot be obtained at the same time. On the other hand, if the metal sulfonate base per polymer exceeds 1000 equivalents / 10 ⁶ g, the solvent solubility of the polyurethane resin will be poor and it will be impractical.

Such a polyurethane resin is produced, for example, by reacting a polyhydroxy compound with a polyisocyanate by a conventional method by using one having a sulfone metal base as a part or all of the polyhydroxy compound. This is as described in JP-A-54-157603 (Japanese Patent Application No. 53-66459).

As described above, the present invention is characterized in that a specific lubricant is used together with the polyurethane resin containing the metal sulfonate group. That is, in the present invention, a lubricant containing a fatty acid having 12 to 18 carbon atoms is used. And the lubricant has a melting point of 12 to 18 carbon atoms and a melting point.
It includes a branched fatty acid ester having a temperature of 10 ° C. or lower and an ester of butyl cellosolve and a fatty acid having 12 to 18 carbon atoms.

The fatty acid used in the present invention has 12 to 18 carbon atoms, preferably 14 to 18 carbon atoms. When the carbon number is lower than 12, the starting torque under high temperature and high humidity is not sufficiently improved, and the carbon number is
When it exceeds 18, blooming is observed, which causes blocking and bit error. Examples of such fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid.

Further, the ester of a fatty acid having 12 to 18 carbon atoms and butyl cellosolve is specifically, n-butyl cellosolve palmitate, n-butyl cellosolve stearate, n-butyl cellosolve oleate, n-butyl cellosolve isostearate, sec-butyl cellosolve palmitate. , Sec-butyl cellosolve stearate, sec-butyl cellosolve arachidinate, tert-butyl cellosolve palmitate, tert-butyl cellosolve stearate, etc. are preferred, with n-butyl cellosolve palmitate and n-butyl cellosolve stearate being preferred.

Examples of the branched fatty acid ester having a melting point of 10 ° C. or less used in the present invention include isobutyl laurate, isobutyl myristate, isobutyl palmitate, isobutyl stearate, 2 ethylhexyl laurate, 2 ethylhexyl myristate, 2 ethylhexyl palmitate, 2 ethylhexyl. Stearate, isotridecyl laurate, isotridecyl myristate, tridecyl palmitate,
Isotridecyl stearate, isocetyl laurate,
Examples include isocetyl myristate, isocetyl palmitate, isocetyl stearate, isostearyl isostearate, n-butyl isostearate, n-butyl isocapronate, and isotridecyl trimethyl acetate. In particular, isotridecyl stearate and isocetyl stearate are preferable.

As a lubricant, one or two of an ester of a fatty acid having 12 to 18 carbon atoms and butyl cellosolve (referred to as C-1 component)
Branched aliphatic ester (C-2
When used together with the component), a magnetic recording medium excellent in durability can be obtained in a wide temperature range. Although the reason is not clear, it is moderately bulky due to the branched alcohol and acid constituting the ester of the C-2 component, has good affinity with the C-1 component, and further It is considered that it also has an appropriate compatibility with the binder and that a necessary and appropriate amount of the lubricant layer is formed on the surface of the coating film (magnetic layer). Further, a combination of a C-2 component having a low melting point and a C-1 component having a high melting point causes leaching of an appropriate amount of the lubricant from a low temperature to a high temperature, and a magnetic recording medium exhibiting excellent durability in a wide temperature range is obtained. It is thought to be obtained. for that reason,
It is estimated to prevent excessive blooming and solve the blocking problem.

When a fatty acid having 12 to 18 carbon atoms (referred to as C-3 component) is added and used to such a lubricating system, durability from low temperature to high temperature and high humidity is further improved and starting torque under high temperature and high humidity is sharply improved. It That is, the addition of the fatty acid lowers the coating surface energy (increases the contact angle), so that the moisture resistance (water) is improved, the starting torque under high temperature and high humidity is reduced, and the durability is improved.

The total amount of lubricant used is generally 2 to 20% by weight based on the magnetic powder.
Is. The blending ratio of the branched ester and butyl cellosolve ester is preferably 70/30 to 30/70 (weight ratio). The fatty acid having 12 to 18 carbon atoms is used in a proportion of 5 to 50%, preferably 10 to 30% (weight) of the total lubricant.

In the present invention, in addition to the polyurethane, a part thereof is nitrocellulose in a range that does not impair dispersibility and durability.
Other binders such as vinyl acetate-based polymers, vinyl chloride-based copolymers, phenoxy, melamine resins and urea resins may be used in combination. In particular, nitrocellulose, vinyl chloride-based copolymer, and phenoxy resin are preferable because they have the effect of improving abrasion resistance at high temperatures. The compounding ratio in this case is 10 to 200%, preferably 20 to 100% with respect to the polyurethane resin of the present invention.
If it exceeds 200%, the coating film becomes rather brittle and the durability is impaired.

Furthermore, in the present invention, a polyisocyanate compound that acts as a crosslinking agent for the binder resin within a range that does not impair the dispersibility of the magnetic powder, for example, a cyclic trimer of hexamethylene diisocyanate (for example, Coronate EH manufactured by Nippon Polyurethane Co.) , Tolylene diisocyanate and trimethylolpropane adduct (for example, Coronate L manufactured by Nippon Polyurethane Co., Ltd.) are preferably added in appropriate amounts (for example, 5 to 60% by weight, preferably 10 to 40% by weight based on the binder resin).

Examples of the ferromagnetic fine particles (magnetic powder) used in the present invention include γ-Fe ₂ O ₃ , CrO ₂ , cobalt ferrite (CoO.Fe ₂ O ₃ ) having a spinel structure, cobalt adsorbed iron oxide, and ferromagnetic Fe- Examples thereof include Co-Ni alloys and fine particles of hexagonal ferrite. Further, fine particles of carbon and / or graphite can be added to the magnetic layer of the present invention in order to enhance conductivity, and other non-magnetic inorganic substances having high hardness (Mohs hardness 6 or more) as an abrasive material. Fine particles such as Cr ₂ O ₃ , Al ₂ O ₃ , SiC and SiO ₂ can be added. Here, the fine particles are particles having a particle size of 0.001 to 2.0 μm.

The non-magnetic support used in the present invention is a polymer such as polyester (particularly a polyester mainly composed of polyethylene terephthalate) or polyphenylene sulfide alone, or a fibrous or powdery reinforcing material or a filler in these polymers. It is appropriately selected from a tape, a film and a sheet-like material made of a material to which is added.

Hereinafter, the present invention will be described more specifically by way of examples. All parts are parts by weight.

〔Example〕

Examples 1 to 6 and Comparative Examples 1 to 4 Component Co Coated γ-Fe ₂ O ₃ (Toda Kogyo) 100 parts Polyurethane resin (Toyobo Byron, sulfonic acid Na group 37
5 Equivalent / 10 ⁶ polymer included) 35 Nitrocellulose (Cell line, Daicel chemistry) 5 Ketjenbrak (Lion Akzo) 6 α-Alumina (Sumitomo Aluminum) 7 Methyl ethylketone 130 Toluene 130 Cyclohexane 130 is kneaded and dispersed in a ball mill for 48 hours. After that, 5 parts of Coronate EH (hexamethylene diisocyanate cyclic trimer; Nippon Polyurethane), 6.5 parts of Coronate L (Tolylene diisocyanate and trimethylolpropane adduct: Nippon Polyurethane) and the lubricant shown in Table 1 were added and uniformly stirred. Dissolved in. After passing the magnetic coating material thus obtained, it was applied onto a 75 μ polyester film using a doctor blade and dried at 80 ° C. for + minutes to form a magnetic coating film having a thickness of about 2 μ. After forming a coating film on the back side in the same manner,
Performs mirror finishing with a heated calender roll, 60 ℃
Heat treatment was performed for 48 hours. Then, the obtained sheet was punched into a disk shape having a diameter of 3.5 inches, the surface was polished, and then the sheet was incorporated into a hard case to obtain a disk cartridge. The disk cartridge was loaded into a Frotpie disk driver and the continuous track durability and starting torque were measured at 50 ° C and 80% RH. The results are shown in Table 1. The durability and starting torque were evaluated by the following methods.

1.Durability The number of passes until the disk driver is continuously driven at 50 ° C and 80% RH with the same track and 75% or less of the initial output or the coating film is destroyed.

2.Starting torque, torque meter MD manufactured by Shinmei Electric Co., Ltd.
Insert the floppy disk into the floppy disk driver with the T2 attached, and let it adhere to the head for 1 hour at 50 ° C and 80% RH, then start the floppy disk driver when rotating. The torque value was measured.

[Advantages of the Invention] As described above, according to the present invention, the sulfonic acid metal group-containing polyurethane blended with the lubricant to which the fatty acid having 12 to 18 carbon atoms is added in an amount of 5 to 50% of the total lubricant is used as the binder. The obtained magnetic recording medium exhibits excellent performance in terms of durability under high temperature and high humidity and reduction of starting torque.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer containing a magnetic powder, a binder and a lubricant is formed on a non-magnetic support, and the binder contains a metal sulfonate group in an amount of 10 to 1000 equivalents / 10 ^6.
Polyurethane resin contained per g polymer is the main component, the lubricant is a fatty acid having 12-18 carbon atoms, a branched fatty acid ester having a melting point of 10 ° C or less, and an ester of butyl cellosolve and a fatty acid having 12-18 carbon atoms. Including and including 12 carbon atoms
A magnetic recording medium, characterized in that the content of the fatty acid of 18 to 18 in the lubricant is 5 to 50% by weight.