JPS6315660B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic recording medium with excellent durability by improving the wear resistance of a magnetic layer. Magnetic powder, binder,
The wear resistance of the magnetic layer formed by applying a magnetic paint consisting of an organic solvent and other necessary components is as follows:
As is well known, it depends on the type of resin used as a binder, and can be improved by incorporating a lubricant into the magnetic layer. Generally, it is prone to wear due to high speed rotation,
Therefore, in magnetic recording disks that require higher wear resistance of the magnetic layer, a mixture of a vinyl chloride-vinyl acetate copolymer and an acrylonitrile-butadiene copolymer is used as a binder for the magnetic layer. It has already been found that it is preferable. The inventors discovered that if a specific lubricant was further mixed into a magnetic layer using this type of binder, the wear resistance could be further improved, and this led to the invention. In other words, this invention incorporates carbon into a magnetic layer using a vinyl chloride-vinyl acetate copolymer (hereinafter abbreviated as VC copolymer) and an acrylonitrile-butadiene copolymer (hereinafter abbreviated as NB copolymer) as binders. The present invention relates to a magnetic recording medium containing 12 to 18 fatty acids. The binder used in this invention is a mixture of a VC copolymer and an NB copolymer, and other resin components may be added as necessary. Examples of the VC copolymer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate-maleic acid copolymer. Commercially available products include VYHH manufactured by UCC,
VAGH and VMCH can be mentioned. Further, as the NB copolymer, any commercially available one can be used regardless of the copolymerization ratio of acrylonitrile and butadiene. A specific example of a commercially available product is Nipole manufactured by Nippon Zeon Co., Ltd.
1432J, Hiker manufactured by Gutsudoritsuchi Chemical Company, USA
1022, hiker 1041, hiker 1042, hiker
1072 etc. Of these two types of copolymers, the VC copolymer contributes to improving the dispersibility of the magnetic powder, while the NB copolymer contributes to increasing the strength of the magnetic layer.
The proportion in which the copolymer is more than 80% by weight and less than 90% by weight, in other words, the latter, that is, the NB copolymer is
The binder is suitable for use in combination in a proportion of 10% by weight or more and less than 20% by weight to improve wear resistance. Note that when the mixture of the VC copolymer and NB copolymer is used as a binder, if a trifunctional low molecular weight isocyanate compound is also used, the strength of the coating film of the magnetic layer is increased and the abrasion resistance is further improved. Specific examples of the trifunctional low molecular weight isocyanate compound include Coronate L manufactured by Nippon Polyurethane Co., Ltd., Desmodyur L manufactured by Bayer,
Examples include Takenate D102 manufactured by Takeda Pharmaceutical Company Limited. The proportion of this compound used is the binder component.
The amount is usually 0 to 5 parts by weight per 100 parts by weight. Examples of fatty acids having 12 to 18 carbon atoms used in this invention include lauric acid, myristic acid, palmitic acid, stearic acid, tridecylic acid, pentadecylic acid, and heptadecylic acid, among which stearic acid is preferably used. Incorporation of these fatty acids into a magnetic layer using a mixture of the VC copolymer and NB copolymer as a binder may be carried out by a conventional method, for example.
A method in which a magnetic layer is formed after kneading the fatty acid described above in a magnetic paint containing a VC copolymer and an NB copolymer as binder components, or a method in which a magnetic layer is formed by kneading a VC copolymer and a NB copolymer that have been previously formed as binder components. The above fatty acid is applied or sprayed onto a magnetic layer containing the above fatty acid in the presence or absence of a solvent such as benzene, toluene, methyl ethyl ketone, methyl isobutyl ketone, or the magnetic layer is immersed in a liquid of the above fatty acid. Just adopt it. In the case of a magnetic recording medium that has a magnetic layer on only one side, such as a magnetic tape, if the above-mentioned dipping method is used, the lubricant liquid will be inside the surface on which the magnetic layer is not formed, that is, on the surface of the substrate such as polyester film. It remains on the surface without being absorbed,
Since this may cause adhesion to the object in contact with the material, the dipping method is not preferable for such single-sided magnetic recording media, and the kneading method is usually adopted. Particularly advantageous. This is because the traditional method of kneading lubricants
When increasing the amount of lubricant mixed in an attempt to obtain higher wear resistance, more lubricant than necessary tends to seep out onto the surface of the magnetic layer due to sliding contact with the magnetic head during recording and playback. This can stain the magnetic head of a recording/reproducing device and cause it to stick to objects it comes in contact with, so normally only a few parts by weight of lubricant can be mixed in per 100 parts by weight of magnetic powder. With this, it was difficult to obtain sufficient wear resistance, but according to the present invention, the amount of this mixture can be increased. That is, it is a mixture of a VC copolymer and an NB copolymer in which the VC copolymer exceeds 80% by weight and
When a mixture ratio of 90% by weight or less is used as a binder and a fatty acid having 12 to 18 carbon atoms is used as a lubricant, when the amount of the above mixture is increased to 15 parts by weight per 100 parts by weight of magnetic powder. However, due to the sliding contact with the magnetic head, no more lubricant than necessary oozes out onto the surface of the magnetic layer, resulting in a remarkable sustained lubrication effect and greatly improved wear resistance. This effect seems to be mainly due to the following two reasons. One of them is that when the proportion of VC copolymer exceeds 80% by weight in a mixed binder of VC copolymer and NB copolymer, the properties as a binder, such as hydrophilicity, are extremely poor. The change occurs to improve the wettability of at least the fatty acid having a hydrophilic group (carboxyl group) in the molecule as the specific lubricant of this invention, and to make this lubricant well compatible with the binder. It is to reach it.
Another reason is that the abrasion strength of the magnetic layer made of this type of binder improves when the VC copolymer accounts for 90% by weight or less of the total, that is, the NB copolymer accounts for 10% by weight or more of the total. It is to come. On the other hand, VC copolymers and NB copolymers, as well as other common resins as binders or other known lubricants such as silicone oils and fluorinated oils, can be used as binders. Even when they are used in combination, if the ratio of their combination deviates from the specified range, problems may arise in terms of the compatibility between the binder and the lubricant or the abrasion strength of the magnetic layer, and the No significant improvement in abrasion resistance was observed. As mentioned above, the fatty acid used in this invention can be used in a very large amount, but it is usually used in an amount of 2 to 15 parts by weight, preferably 2 to 10 parts by weight, per 100 parts by weight of magnetic powder. Next, the present invention will be explained in more detail with reference to Examples. In addition, in the following, parts are shown as parts by weight. Example 1 100 parts of γ-Fe ₂ O ₃ powder, VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, mentioned above) 27
parts, 5 parts of Nipol 1432J (NB copolymer, above),
A magnetic paint was prepared by kneading and dispersing a mixture of 10 parts of stearic acid, 10 parts of carbon black, 135 parts of toluene, and 135 parts of methyl isobutyl ketone in a ball mill for about 70 hours. This paint was applied to one side of a 188 μm thick polyester film to a dry thickness of approximately 10 μm, and dried to form a magnetic layer. Next, the surface of this magnetic layer was polished to a mirror finish using a calendar roll heated to about 80° C., and then punched into a disk shape (about 65 mm in diameter) to obtain a magnetic disk. Example 2 A magnetic paint was prepared in the same manner as in Example 1, except that lauric acid was used instead of stearic acid in Example 1, and 1.7 parts of Coronate L (trifunctional low molecular weight isocyanate compound, described above) was added. A magnetic disk was obtained in the same manner as in Example 1 using this paint. Comparative Example 1 A magnetic disk was obtained in exactly the same manner as in Example 1, except that silicone oil, which is known as another conventional lubricant, was used instead of stearic acid in Example 1. Comparative Example 2 A magnetic disk was obtained in exactly the same manner as in Example 1, except that fluorine oil, which is known as a conventional lubricant, was used instead of stearic acid in Example 1. Comparative Example 3 A magnetic disk was obtained in exactly the same manner as in Example 1 except that 5 parts of dioctyl phthalate was used in place of 5 parts of Nipole 1432J in the magnetic paint of Example 1. Comparative Example 4 A magnetic disk was obtained in exactly the same manner as in Example 1, except that the number of copies of VAGH used was changed to 20 parts, and the number of parts used of Nipole 1432J was changed to 13 parts. Comparative Example 5 A magnetic disk was obtained in exactly the same manner as in Example 1, except that the number of copies of VAGH used was changed to 31 parts, and the number of copies used of Nipole 1432J was changed to 2 parts. The magnetic disks of Examples 1 to 2 and Comparative Examples 1 to 5 were each loaded into a recording/reproducing device, and the magnetic disks were placed in sliding contact with a magnetic head (pad pressure of 40 g/cm ² ) for about 1 hour.
It was run at a speed of m/sec, and the running time until the cumulative number of dropouts reached 500 was measured. The results obtained and the surface condition of the magnetic layer are shown in the table below. Note that VC (weight %) in the table means the weight % of VAGH in the total amount of VAGH and Nipole 1432J.

[Table] As is clear from the above table, according to this invention, a VC copolymer and an NB copolymer are used together as a binder in a specific ratio, and a fatty acid having 12 to 18 carbon atoms is used as a lubricant. It can be seen that the wear resistance of the magnetic layer is improved and the durability of the magnetic disk is greatly improved. On the other hand, magnetic disks using silicone oil (Comparative Example 1), fluorine oil (Comparative Example 2) as a lubricant, or only VC copolymer (Comparative Example 3) as a binder were fully satisfactory. Doesn't show the durability you get. Also, V.C.
Even when using copolymer and NB copolymer together,
When the proportion of VC copolymer used was 80% by weight or less (Comparative Example 4) and when the proportion of VC copolymer used exceeded 90% by weight (Comparative Example 5), the effect of improving durability was still obtained. do not have.

Claims (1)

[Scope of Claims] 1. A mixture of a vinyl chloride-vinyl acetate copolymer and an acrylonitrile-butadiene copolymer in which the former has a mixing ratio of more than 80% by weight and less than 90% by weight is considered magnetic. A magnetic recording medium comprising a magnetic layer containing a fatty acid having 12 to 18 carbon atoms as a powder binder. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer contains a trifunctional low molecular weight isocyanate compound.