JPS6034168B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a substrate (for example, a polyethylene terephthalate film) and a magnetic layer (
That is, the present invention relates to a magnetic recording medium, particularly a magnetic tape, comprising a magnetic recording layer containing magnetic powder, bisodar, etc.

Conventionally, a back layer containing carbon black or the like is formed on the back surface of this type of magnetic tape, thereby reducing the charging property.

On the contrary, however, carbon black or the like causes unevenness on the back surface, and when the magnetic tape is wound, such unevenness is transferred to the magnetic layer on the surface, causing output fluctuations. The present invention has been made to correct such defects, and in the magnetic recording medium mentioned at the beginning, a layer (i.e., a back layer) containing a conductive acrylic resin and a polyisocyanate compound is formed on the other side of the substrate. This relates to a magnetic recording medium characterized in that the magnetic recording medium is formed on the surface of the magnetic recording medium.

With this configuration, the amount of charge (electrical resistance)
It is possible to reduce the output voltage and provide a device without (dropout) due to output fluctuation. According to the present invention, poly(2-hydroxy-3-methacryloxypropyltrimethylammonium chloride) having the following structural formula is desirable as the above-mentioned conductive acrylic resin.

Since this conductive acrylic resin has ionic trimethylammonium chloride at the branch end, it has excellent conductivity and contributes to lowering the amount of charge (electrical resistance) of the back layer.

Furthermore, -OH in the branches of this conductive acrylic resin reacts and bonds with the isocyanate group of the polyisocyanate compound, producing a polyisocyanate-modified acrylic copolymer (crosslinked polymer) with high wear resistance. As a result, the abrasion resistance of the back layer is greatly improved. Since the back layer according to the present invention can be composed of such a copolymer, it is not necessary to add particles such as carbon black as in the conventional case, and therefore the surface of the back layer becomes mirror-finished, and output fluctuations due to unevenness do not occur. It is. Further, in the present invention, since it is only necessary to prepare a polymer solution without adding carbon black or the like, the time for mixing the back coat material can be greatly shortened, and workability can be improved. Note that this conductive acrylic resin may be poly(2-hydroxy-3-acryloyloxylopyl trimethylammonium chloride) in addition to the above-mentioned methachloro resin.

Further, the above-mentioned conductive acrylic resin may be a copolymer of the above-mentioned -OH-containing conductive acrylic resin and a conductive acrylic resin having the following structural formula (without monoOH),
Although the latter resin has ionic properties, it does not react with isocyanate, so its proportion to the copolymer is preferably about 50% or less (that is, to the extent that the former resin provides wear resistance). In addition, the average molecular weight of the above-mentioned conductive acrylic resin is preferably from 20,000 to 200,000, and even more preferably from 40,000 to 100,000.

Further, as the polyisocyanate compound that can be used in the present invention, the following di-, tri-, and tetra-isocyanates can be used. Aliphatic isocyanate having a cyclic group, aromatic nucleus isocyanate, naphthalene, sonbiphenylisonanate, borisonane of citri and tetraisocyanate, and other isocyanates include RP○(NCO)2
Organic phosphorus isocyanates such as CF3NCO or CnF
Fluorinated isocyanate such as 2n10, C ratio NCO, RS02
Examples include sulfonyl isocyanate such as NCO, isocyanate of benzyl chloride, isocyanate of benzalkroid, isocyanate of ethylbenzole, isocyanate of styrene, urethane triisocyanate, and the like.

In the back layer according to the present invention containing the above-mentioned polyisocyanate compound and the above-mentioned conductive acrylic resin, the polyisocyanate compound is contained in a ratio of 5 to 50 parts by weight based on 100 parts by weight of the conductive acrylic resin. Preferably, the proportion is 10 to 3 parts by weight.

That is, if the amount of the polyisocyanate compound is less than 1 part by weight, the proportion of the isocyanate-modified acrylic copolymer will be small, resulting in poor wear resistance, and if it exceeds 5 parts by weight, the material will be too crosslinked and become too hard. However, the relative proportion of the conductive acrylic resin decreases, and the ionicity (conductivity) as a whole becomes weaker. The back layer of the magnetic recording medium according to the present invention may contain additive components other than the above-mentioned conductive acrylic resin.

This additive component may be a resin in an amount of 5 parts by weight or less based on 10 parts by weight of the conductive acrylic resin, and includes piny chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, chloride Vinyl-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride Copolymer, ester methacrylate styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer Polymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, polyvinyl acetal,
Examples include cellulose derivatives, styrene-butadiene copolymers, polyester resins, phenol resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea formaldehyde resins, and the like. A magnetic recording medium, for example a magnetic tape, according to the present invention may have the configuration shown in the drawings.

That is, the above-described back layer 3 according to the present invention is coated on the back surface of a poly-IJ ethylene terephthalate substrate 2 having a normal surface magnetic layer 1.

The thickness of this back layer after drying is preferably 0.1 to 5 mm.
Even better is 0.2 to 3 Buddhas, for example about 2 Buddhas. If the thickness of the back layer 3 is less than 0.1 mm, it will be too thin and the conductive effect will be poor, and if it exceeds 5 r, the tape will become too thick, which is not preferable. Further, as a solvent for coating the back layer 3, conventionally known solvents can be used, including cyclofoxanone, dimethylformamide, methyl ethyl ketone, and the like. Next, embodiments of the present invention will be described in more detail.

Comparative example 1 The following backcoat composition was prepared.

Carbon black (Asahi Carbon #35) 10 parts by weight Polyester resin 100 Cyclohexanone 300 Dimethylformamide 100 Disperse this mixture in a ball mill to make a coating, and apply it to the back surface of the magnetic tape in a thickness of 1 to 3 mm. It was coated and dried.

Comparative example 2 The following backcoat composition was prepared.

Carbon black (Asahi Carbon #35) 75 parts by weight Silica gel 25 Polyester resin 100 Cyclohexanone 300 Dimethylformamide 100 This mixture was applied to the back surface of a magnetic tape in the same manner as in Comparative Example 1 and dried to form a back layer. .

EXAMPLES The following backcoat compositions were prepared.

Conductive acrylic resin 10 parts by weight Polyisocyanate (Desmodyur L) 20 Cyclohexanone 100 Methyl ethyl ketone 300 This mixture was easily obtained by solution mixing without mixing in a ball mill.

Then, this mixture was coated and dried on a substrate in the same manner as above to form a back layer, and a back layer in which the conductive acrylic resin was crosslinked with isocyanate was obtained. When the surface roughness and electrical resistance of the back layer obtained as described above were measured, the following results were obtained.

The roughness was measured using a stylus, and the electrical resistance was measured by measuring the resistance between both electrodes with a magnetic tape suspended between them. In addition, each sample tape was wound forward (FF) and rewinded (RW) 20 times back and forth, and 40qo.
Store at 80%RH for 4 hours, then record and play.
When the output fluctuations were measured, the following results were obtained. As is clear from the above results, the magnetic tapes of Comparative Examples 1 and 2 have large output fluctuations due to the FF and RW winding operations, whereas the magnetic tapes of this example have output fluctuations before and after the winding operations. It can also be seen that the difference in the amount of wear is small and that the back layer has good abrasion resistance.

[Brief explanation of drawings]

The drawing is a cross-sectional view of a magnetic tape according to an embodiment of the present invention. In addition, in the symbols used in the drawings, 1...magnetic layer, 2...substrate, 3...back layer.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a substrate and a magnetic layer formed on one surface of the substrate, in which a layer containing a conductive acrylic resin and a polyisocyanate compound is formed on the other surface of the substrate. A magnetic recording medium characterized by: