JPS5891525A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with superior mechanical strength, electric characteristics and durability by using specified polyurethane resin as one component of a binder for forming a magnetic layer. CONSTITUTION:A magnetic recording mudium is obtd. by forming a magnetic layer on a substrate such as a polyester film using a binder cnsisting of polyurethane resin and vinyl chloride-vinyl acetate copolymer, vinylidene chloride resin, phenoxy resin or acrylic resin or further contg. an isocyanate compound with low mol. wt. 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 specifically to a magnetic recording medium KH such as a magnetic tape which has excellent mechanical strength, electrical properties and durability.

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, as the thickness of the magnetic tape becomes thinner, the mechanical strength of the tape becomes weaker, so during recording, playback, fast forwarding, rewinding, and unloading, the edges of the magnetic tape must be used to restrict the running of the magnetic tape using a loading post, etc. The magnetic tape regulating flange of the guide member may come into contact with the magnetic tape regulating flange and breakage may occur, and curling or wrinkles are likely to occur.

Magnetic tapes with improved mechanical strength have been proposed, such as by using reinforcing films stretched in the length direction during the production of plastic films such as polyester films as the base of magnetic tapes, etc. This is not sufficient and it is not possible to effectively prevent breakage and curling of the edge portion of the magnetic tape.

In view of the current situation, the inventors generally developed magnetic powder,
As a result of various studies focusing on the magnetic layer of a magnetic recording medium, which is made by coating and drying a magnetic paint consisting of a binder component, an organic solvent, and other necessary components, we found that the binder component of the magnetic layer can be used as a binder component. , a polyurethane resin containing one selected from vinyl chloride-vinyl acetate copolymers, vinylidene chloride resins, phenoxy resins, and acrylic resins, and 4,4'-diphenylmethane diisocyanate in a composition ratio of 15 weight beak or more. When used in combination, the elastic modulus of the magnetic layer becomes even higher, and the mechanical strength of the magnetic tape is sufficiently improved, and even if the thickness of the magnetic tape is reduced, breakage and curling of the magnetic tape edges can be effectively prevented. At the same time, the present inventors discovered that the dispersibility and abrasion resistance of the magnetic powder were also improved, and a magnetic recording medium with excellent electrical properties and durability could be obtained, leading to the present invention.

The polyurethane resin used in this invention is a polyurethane resin containing 4,4'-diphenylmethane diisocyanate as an isocyanate component in a composition ratio of 15 parts by weight or more; -butanediol,
It is produced by synthesizing a polyester from a diol such as 1,6-hexanediol and reacting this polyester with 4,4'-diphenylmethane diisocyanate.

This Mari's polyurethane resin has a straight chain 4.4 urethane resin in which two benzene nuclei are linearly bonded via a methylene group as an isocyanate component, and an isocyanate group is bonded to the para position of both benzene nuclei. - Contains diphenylmethane diisocyanate at a composition ratio of 15 parts by weight or more, so the elastic modulus of the magnetic layer is further increased by the action of linearly bonded benzene nuclei of the isocyanate component contained in a large amount, resulting in strong magnetic properties. The layer is formed and the mechanical strength of the magnetic tape is further improved.0 On the other hand, even if conventional polyurethane resins contain 4,4'-diphenylmethane diisocyanate as an isocyanate component, the content ratio is only 15%. Since the weight is less than 100 g, the action of the linearly bonded pentene 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.

In addition, vinyl chloride-vinyl acetate copolymer used in combination,
Vinylidene chloride resin, phenoxy resin, and acrylic resin all have good affinity with magnetic powder.IFC magnetic powder has excellent dispersibility and improves electrical properties.
By forming a hard magnetic layer, wear resistance is also improved. In addition, these resins have hydroxyl groups or carboxyl groups in their molecules, so when they are used together with low molecular weight isocyanate compounds, the hydroxyl groups or carboxyl groups react with the isocyanate groups in the low molecular weight isocyanate compounds and cause crosslinking. , the coating strength of the magnetic layer is strengthened and the abrasion resistance is further improved.

Vinyl chloride-vinyl acetate copolymers used in combination include vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate copolymers, and vinyl chloride-vinyl acetate-maleic acid copolymers. copolymers, etc., and a specific example is VAGH manufactured by U, C, C in the United States.
,VYHH.

Examples of vinylidene chloride-based resins include vinylidene chloride resin, vinylidene chloride-acrylonitrile copolymer, and vinyl chloride. -Vinylidene chloride copolymer, etc., and specific examples include Dioaan 207D-C manufactured by Pardish Co., Ltd., Saran F-216 manufactured by Asahi Dow Company, F-
120, F-220, F-300, F-310, Denka 100OWK manufactured by Denki Kagaku Kogyo Co., Ltd., Aron 321 manufactured by Toagosei Kagaku Co., Ltd., and the like. Further, as a specific example of the phenoxy resin, PKHH manufactured by U, C, C, USA.

PKHCSPKHA, etc., and examples of acrylic resins include polyacrylic esters, polymethacrylic esters, polyacrylonitrile, polythalylamide, etc., and specific examples include Acrynal 1000 manufactured by Toei Kasei Co., Ltd. It will be done.

The ratio of vinyl chloride-vinyl acetate resin, vinylidene chloride resin, phenoxy resin or acrylic resin to the polyurethane resin containing the above-mentioned 4,4'-diphenylmethane diisocyanate in a composition ratio of 15% by weight or more is 90% by weight. It is preferable that the ratio is within the range of 10 to 10 to 90. If the ratio of the polyurethane resin used is too small, the elastic modulus of the magnetic layer cannot be sufficiently improved, and if it is too large, the dispersibility of the magnetic powder may be impaired. There is.

In this invention, the low molecular weight isocyanate compound used in combination is usually 1 mol of Doriol and 3
A trifunctional low molecular weight isocyanate compound obtained by reacting with mol of diisocyanate is preferably used, and when this type of isocyanate compound is used in combination, the isocyanate group contained in the isocyanate compound is converted to the vinyl chloride. - Crosslinking occurs by reacting with hydroxyl groups or carboxyl groups contained in molecules of vinyl acetate copolymers, phenoxy resins, acrylic resins, etc., further increasing the coating strength of the magnetic layer and improving wear resistance. will improve further. Specific examples include, for example, Kopune) L S Kolone) HL, Koshi ↑-) 2036, manufactured by Nippon Polyurethane Industries, Ltd., Dainippon Ij, Koshi ↑-)
/ 7 l D 750 s, Ieni Co., Ltd.'s De8 Module L1, Takeda Pharmaceutical Co., Ltd.'s Takene) D102 Kamedo. 0.1~ based on the total amount of your binder components used
It is preferable that the amount is within the range of 30% by weight. If it is too small, the crosslinking density will be low and the coating strength will be weakened, resulting in poor wear resistance. If it is too large, the crosslinking density will be high and the magnetic layer will become hard.
It may make it brittle.

Examples of the magnetic powder used in this invention include r-F
e20. Powder, Fe, O, powder, Co-containing r-Fe2
In addition to 0° powder, Co-containing Fe powder, 04 powder, and Cr 02 powder, various conventionally known magnetic powders are widely included, such as metal powders such as Fe powder, CO grain powder, and Fe-Ni powder.

Examples of organic solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone; ester Ja agents such as ethyl acetate and butyl acetate; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; There are no particular restrictions on the solvent used to dissolve the binder component, such as amide solvents, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran, and dioxane, and the solvents used may be used alone or in combination of two or more. used.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, etc. may be added to the material.

It may be carried out according to the conventional KFi method for manufacturing the magnetic recording medium of the present invention. For example, vinyl chloride-vinyl acetate is added to a polyurethane resin containing the above-mentioned 4,4-benzene diphenylmethane diisocyanate in a composition ratio of 15% by weight or more. It contains one selected from polyester copolymers, vinylidene chloride resins, phenoxy resins, and acrylic resins, and optionally low molecular weight isocyanate compounds, as well as magnetic powder, organic solvents, and other additives. It is sufficient to prepare a magnetic coating material, apply it onto a substrate such as a polyester film by a suitable method such as spraying or coating, and dry it.

Next, one embodiment of the present invention will be described.

Example I Co-coated r-Fe20S magnetic powder 100 parts by weight Granular σ-Fe20B powder 4 parts by weight Carbon black 41 Zinc stearate 0.51 Polyurethane resin (4,4
VAGH (vinyl alcohol copolymer made from vinyl chloride 15 manufactured by U.C.C. in the United States) stearin-n'-butyl 11 Myristic acid 0.5# cyclohexanone 95 l toluene
95 l.

This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint. This magnetic paint was applied to a polyester film having a thickness of 10 .mu.m to a dry thickness of 5 .mu.m. After drying and surface treatment, the film was cut to a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, f-y
A magnetic tape was prepared in the same manner as in Example 1, except that 5 parts by weight of Cinate L (a trifunctional low molecular weight isocyanate compound manufactured by Nippon I Diurethane Kogyo Co., Ltd.) was added.

Example 3 A magnetic coating was prepared in the same manner as in Example 1 except that the same amount of Saran F-216 (vinylidene chloride-acrylonitrile copolymer manufactured by Salt Dow Co., Ltd.) was used in place of VAGH in the composition of the magnetic paint in Example 1. I made a tape.

Example 4 In the composition of the magnetic paint in Example 1, VAGHK
Instead, PKHH (phenoxy resin manufactured by U, C, C, USA)
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of each was used.

Example 5 A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of Acrynal 1000 (methacrylic acid ester manufactured by Toei Kasei Co., Ltd.) was used in place of VAGH in the composition of the magnetic paint manufactured by Example IK. Ivy.

Comparative Examples 1 to 5 In the composition of the magnetic paint in each example, the polyurethane resin of Example 1 was replaced with 4,4'-diphenylmethane diisocyanate at a content of 133 parts by weight. The same amount of polyurethane resin was used in each example. A magnetic tape was prepared in the same manner as in the example, using binder resins shown in Table 1 below as binder components other than the polyurethane resin.

Table 1 For the magnetic tapes obtained in each example and each comparative example, the elastic modulus at X% elongation of the magnetic layer was measured, and each magnetic tape was wound 345 m into a VH5 video cassette to examine the mechanical strength. After loading the tape into a VH5 video tape recorder, the tape was run 30 Gm from the beginning, and the tape stopped running. At this point on the tape, the tape was loaded and unloaded 10 times from the rotating cylinder head, and then the moving tape guide was used. The degree of damage to the tape edge was observed. Further, the audio output of each magnetic tape was measured using the same video deck, and the audio output of the magnetic tape obtained in Example 1 was defined as O, and the difference was expressed as O.

Table 2 below shows the results.

As is clear from the upper table of Table 2, the magnetic tapes obtained according to the present invention (Examples 1 to 5) all have a higher elastic modulus of the magnetic layer than the magnetic tapes obtained in Comparative Examples 1 to 5. As a result, edge breakage was observed in the magnetic tapes obtained in Comparative Examples 1 to 5, and the audio output was extremely poor, whereas no abnormality was observed in any of the magnetic tapes obtained by this invention. , It can be seen that the mechanical strength of the magnetic recording medium obtained by the present invention is further improved.

Claims (1)

[Claims] 1. As a binder component, one selected from vinyl dichloride-vinyl acetate copolymer, vinylidene chloride resin, phenoxy resin, and acrylic resin, and 4,4'-diphenylmethane diisocyanate. A magnetic recording medium 2 having a magnetic layer comprising a polyurethane resin containing a composition ratio of 15 parts by weight or more.A magnetic recording medium according to claim 1, further comprising a low molecular weight isocyanate compound as a binder component. magnetic recording medium