JPS5891524A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with superior mechanical strength by using specified polyurethane resin as a binder for forming a magnetic layer. CONSTITUTION:A magnetic recording medium is obtd. by forming a magnetic layer on a substrate such as a polyester film using polyurethane resin as a binder. The polyurethane resin contains >=15wt% straight chain 4,4'-diphenylmethane diisocyanate as an isocyanate component. The diisocyanate has 2 benzene rings bonded together through a methylene group in the form of a straight chain and isocyanate groups bonded to the p-positions of both the benzene rings.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape having excellent mechanical strength.

In recent years, attempts have been made to make the thickness of magnetic tapes as thin as possible, particularly for video magnetic tapes, in order to lengthen the recording and playback time as much as possible when assembled in a cartridge case. However, if the thickness of the magnetic tape is made thinner (the mechanical strength of the tape will be weakened, the edge part of the magnetic tape will become magnetic when recording, playing, fast-forwarding, rewinding, loading, unloading, etc.). The guide member that regulates the running of the tape may come into contact with the magnetic tape regulating flange edge and break, and it also tends to curl or wrinkle.

For this reason, attempts have been made to improve the mechanical strength of magnetic tapes by using doubled films stretched in the longitudinal direction at °C as substrates for magnetic tapes during the production of plastic films such as polyester films, but this is still not sufficient. Otherwise, breakage and curling of the magnetic tape edge portion cannot be effectively prevented.

In view of the current situation, the inventors generally developed magnetic powder,
As a result of extensive research focusing on the magnetic layer of a magnetic recording medium, which is produced by applying a magnetic paint consisting of a binder component, an organic solvent, and other necessary components onto a substrate and drying it, we found that the binder for the magnetic layer When a polyurethane resin containing 4,4'-diphenylmethane diisocyanate at a composition ratio of 15 parts by weight or more is used as a component, the elastic modulus of the magnetic layer is further increased, and as a result, the mechanical strength of the magnetic tape is sufficiently improved. However, the inventors have discovered that even if the thickness of the magnetic tape is reduced, breakage and curling of the magnetic tape edge can be effectively prevented, and the present invention has been completed.

The polyurethane resin used in this invention is a polyurethane resin containing a combination of 15 or more by weight of 4,4'-diphenylmethane diisocyanate as an isocyanate component, for example, a dibasic acid such as adipic acid and 1,4 It is produced by synthesizing polyester from diols such as -butanediol and 1,6-hexanediol, and then reacting this polyester with 4,4'-diphenylmethane diisocyanate.

This type of polyurethane resin has, as an isocyanate component, two benzene nuclei bonded in a linear chain via a methylene group, and an isocyanate group bonded to the para position of both benzene nuclei. '-Diphenylmethane diisocyanate is contained in a composition ratio of 15 kg or more in total, so the elastic modulus of the magnetic layer is further increased by the action of linearly bonded benzene nuclei of the isocyanate component containing a large amount of V, making it strong. Even if a magnetic layer is formed and contains 4,4'-diphenylmethane diisocyanate as an isocyanate component, if the content is less than 15% by weight, linearly bonded benzene Since the action of the nuclei is insufficient, the elastic modulus of the magnetic layer is not so high, and the mechanical strength of the magnetic tape is not sufficiently improved.

Such a polyurethane resin containing 4,4'-diphenylmethane diisocyanate as an isocyanate component in a composition ratio of 15% by weight or more may be used alone, but it may also be used in combination with various other binder components. For example, when used in combination with vinyl chloride-vinyl acetate copolymer, vinylidene chloride thread resin, phenoxy resin, etc., the dispersibility and abrasion resistance of magnetic powder are improved, and mechanical strength as well as electrical properties and durability are improved. A magnetic recording medium is obtained. Vinyl chloride used in combination in this way
Examples of the vinyl acetate copolymer include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, etc. Specific examples include United States U, C, C
Company-made VAGH.

VY) I) TSVMCH, Eslec A1 Eslec C1 Eslec M manufactured by Tanemizu Kagaku Kogyo Co., Ltd., and Denkavinyl manufactured by Kei Kagaku Kogyo Co., Ltd., and the like. A specific example of the phenoxy resin is PKH) manufactured by U, C, C, USA.

Examples include PKHC and PKHA. In addition to vinylidene chloride resins, examples of vinylidene chloride resins include vinyl chloride-acrylonitrile copolymers, vinyl chloride-vinylidene chloride copolymers, etc.
Saran F-216, F-120, F-220 manufactured by Shio Dow
, F-300, F-310, Denka i manufactured by Denki Kagaku Kogyo Co., Ltd.
ooowK.

Examples include Aron 321 manufactured by Toagosei Kagaku Co., Ltd.

Examples of the magnetic powder used in this invention include r
Fe2Og powder, Fe, 04 powder, Co-containing -Fe2
In addition to 0B powder, Co-containing Fe3O4 powder, and CrO2 powder, various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni powder are widely included. Ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as toluene and xylene, acid amide solvents such as dimethylformamide, dimethyl sulfoxide, etc. Solvents suitable for dissolving the binder component to be used, such as sulfoxide solvents, tetrahydro-7rane, and ether solvents such as dioxane, can be used alone or in combination of two or more without particular restriction. Various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

It may be carried out according to the conventional ttcd method for manufacturing the magnetic recording medium of the present invention, and even if 4,4'-diphenylmethane diisocyanate-F is used as the above-mentioned isocyanate t4,
If necessary, other binder components are added to the polyurethane resin containing a composition ratio of 5 parts by weight or more, and further magnetic powder,
A magnetic paint containing an organic solvent, agent and other additives may be prepared, applied onto a substrate such as a polyester film by any means such as spraying or roll coating, and dried.

Next, embodiments of the invention will be described.

Example I Co coated r-Fe20. Magnetic powder ioo parts by weight Carbon black ・41 Polyurethane resin (4,4'-di7-25 to rutane diisocyanate content 20 parts by weight) Myristic acid 0,5I cyclohexanone 95 l Toluene
A magnetic paint was prepared by mixing and dispersing 95 liters of this composition in a ball mill for 72 hours. This magnetic paint was applied to a polyester film having a thickness of 101 .mu.m with a KIk cloth to a dry thickness of 5 .mu.m. After drying and surface graining, the film was cut to a predetermined width to produce a magnetic tape.

Example 2 The composition of the magnetic paint in Example 1 was the same as Example 1 except that the polyurethane resin of Example 1 was replaced with the same amount of polyurethane resin containing 17% by weight of 4,4'-diphenylmethane diisocyanate. A magnetic tape was made in the same manner. Example 3 In the composition of the magnetic paint in Example 1, VA
Added 15 parts by weight of GH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer manufactured by U, C, C, USA), and increased the amount of polyurethane resin IIN (content of 4,4'-diphenylmethane diisocyanate 20% by weight) to 25 parts by weight. A magnetic tape was produced in the same manner as in Example 1 except that parts by weight were changed to 10 parts by weight.

Comparative Example 1 A magnetic tape was prepared in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of polyurethane resin containing 4,4-diphenylmethane diisocyanate was used as the polyurethane resin, with a content of 13% by weight. I made it.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 3, except that in the composition of the magnetic paint in Example 3, the same amount of polyurethane resin containing 1031% of 4,4'-diphenylmethane diisocyanate was used as the polyurethane resin. I made it.

For the magnetic tapes obtained in each example and each comparative example, the elastic modulus of the magnetic layer at one elongation was measured, and in order to increase mechanical strength, each magnetic tape was wound into a VH5 video cassette for 300 m. After being loaded into a VH5 video tape recorder, the tape is run and stopped approximately 10 meters from the end of the tape, and the tape is loaded and unloaded from the rotating cylinder head five times at this location on the tape. The degree of damage to the tape edges caused by the guide was observed, and the audio output of each magnetic tape was measured using the same video deck. Note that the measured value of the audio output was expressed as a relative value with respect to the audio output of the companion magnetic tape obtained in Example 1, which was set as 0.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained in the present invention (Examples 1 to 3) all have higher elastic modulus of the magnetic layer than the magnetic tapes obtained in Comparative Examples 1 and 2. Results: While the magnetic tapes obtained in Comparative Examples 1 and 2 had broken edges and the audio output was extremely poor, no abnormality was observed in any of the magnetic tapes obtained by the present invention. It can be seen from this that the mechanical strength of the magnetic recording medium obtained by the present invention is further improved.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer comprising a polyurethane resin containing 4,4'-diphenylmethane diisocyanate in a composition ratio of 15 or more as a binder component.