JPS6315658B2 - - 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 simply referred to as VC copolymer) and an acrylonitrile-butadiene copolymer (hereinafter simply referred to as NB copolymer) as binders. The present invention relates to a magnetic recording medium containing a fatty acid ester having a total carbon number of 13 to 36 derived from several dozen or more 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. 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. , in other words, the latter, that is, NB
When the copolymer is used in a proportion of 10% by weight or more and less than 20% by weight, the binder is suitable for improving 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.
It is usually within the range of 0 to 5 parts by weight per 100 parts by weight. The fatty acid esters derived from fatty acids having 12 or more carbon atoms used in this invention have a total number of carbon atoms of 13 to 36, but particularly preferred are n-butyl stearate, dodecyl laurate, and propyl palmitate. , amyl palmitate, propyl oleate, etc., with a total carbon number of 19 to 24. Incorporation of these fatty acid esters into a magnetic layer using a mixture of the VC copolymer and NB copolymer as a binder can be carried out by a conventional method. A method of forming a magnetic layer after kneading the above fatty acid ester in a magnetic paint containing as a binder component, or adding the above fatty acid ester to a magnetic layer containing a previously formed VC copolymer and NB copolymer as a binder. toluene,
The magnetic layer may be coated or sprayed in the presence or absence of a solvent such as methyl isobutyl ketone or cyclohexanone, or the magnetic layer may be immersed in the fatty acid ester solution. 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
Using a binder with a mixing ratio of 90% by weight or less, a fatty acid with a carbon number of 1 to 5 and a carbon number of 12 or more is used as a binder.
When using an alkyl ester as a lubricant, even when the above amount is increased to 15 parts by weight per 100 parts by weight of magnetic powder, more lubricant than necessary oozes out onto the surface of the magnetic layer due to sliding contact with the magnetic head. It exhibits a remarkable long-lasting lubrication effect and greatly improves wear resistance. This effect seems to be mainly due to the following two reasons. One is that in a mixed binder of VC copolymer and NB copolymer, the VC copolymer accounts for 80% by weight of the total.
When the ratio exceeds 100%, an extreme change appears in the properties as a binder, such as hydrophilicity, and at least the wettability of the fatty acid ester which also has a hydrophilic group (ester group) in the molecule as the specific lubricant of this invention is observed. The purpose is to improve the properties of the lubricant and to make the lubricant well compatible with the binder. 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 fluorine oils, Even when used in combination, if the ratio of the combined use exceeds 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 ester used in this invention can be used in a very large amount, but it is usually 2 to 15 parts by weight, preferably 2 to 15 parts by weight, per 100 parts by weight of magnetic powder.
It may be used within a range of 10 parts by weight. Next, the present invention will be explained in more detail with reference to Examples. In addition, in the following, parts indicate parts by weight. Example 1 100 parts of γ-Fe ₂ O ₃ powder, VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, described above) 27
parts, N1432J (NB copolymer, trade name manufactured by Nippon Zeon Co., Ltd.) 5 parts, n-butyl stearate 10 parts
After kneading and dispersing a mixture of 10 parts of carbon black, 135 parts of toluene, and 135 parts of methyl isobutyl ketone in a ball mill for about 70 hours, 1.7 parts of Coronate L (isocyanate compound, trade name manufactured by Nippon Polyurethane Co., Ltd.) was added to the mixture. Add
The mixture was further dispersed for about 1 hour to prepare a magnetic paint. This paint was applied to one side of a 188 μm thick polyester film to a dry thickness of about 10 μm, and dried to form a magnetic layer. Next, the surface of this magnetic layer was mirror-finished with a calendar roll heated to about 80° C., and then punched out into a disk shape (diameter about 65 m/m) to obtain a magnetic disk. Example 2 A magnetic disk was obtained in the same manner as in Example 1 except that propyl palmitate was used instead of n-butyl stearate. 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 a conventional lubricant, was used instead of n-butyl stearate. 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 n-butyl stearate 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 instead of 5 parts of N1432J in the magnetic paint of Example 1. Comparative Example 4 Example 1 except that the number of copies used for VAGH was changed to 20 copies, and the number of copies used for N1432J was changed to 13 copies.
A magnetic disk was obtained in exactly the same manner. Comparative Example 5 Example 1 except that the number of copies used for VAGH was changed to 31 copies, and the number of copies used for N1432J was changed to 2 copies.
A magnetic disk was obtained in exactly the same manner. 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. In addition, VC (weight%) in the table refers to VAGH and
It means the weight percent of VAGH in the total amount with N1432J.

[Table] As is clear from the above table, VC copolymer and NB copolymer are used together in a specific ratio as a binder, and the total number of carbon atoms derived from fatty acids with 12 or more carbon atoms is 13 or more as a lubricant. It can be seen that according to this invention, which uses No. 36 fatty acid ester, the abrasion 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 in which a magnetic layer serving as a powder binder contains a fatty acid ester having a total of 13 to 36 carbon atoms derived from a fatty acid having 12 or more carbon atoms. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer further contains a trifunctional low molecular weight isocyanate compound.