JPS59132417A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium maintaining its high performance for a long term by incorporating a dispersant represented by a specified general formula into a magnetic layer. CONSTITUTION:Particles of gamma-Fe2O3, Fe3O4 contg. Co or gamma-Fe2O3 coated with Co are used as representative magnetic particles. A liq. for forming a magnetic layer is prepd. by adding at least one kind of dispersant represented by the general formula (where R is H or methyl, and n is 1 or 2) by 1-10wt% of the amount of magnetic particles. When the dispersant is added by <1wt%, its effect can not be shown sufficiently. When the dispersant is added by >10wt%, the relative amount of the magnetic particles is reduced, exerting unfavorable influence on the magnetic characteristics. It is preferable that the resulting magnetic layer contains suitable additives such as an antistatic agent, a lubricant and an abrasive material besides a binder, the magnetic particles and the dispersant.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which a specific compound (phosphate ester compound) is used as a dispersant added to a magnetic layer.

BACKGROUND OF THE INVENTION It is known that magnetic recording media, typified by magnetic tapes, floppy disks, etc., include those in which a magnetic layer containing magnetic particles and J inder as main components is provided on a non-magnetic support such as Silasnac.

In manufacturing this type of magnetic recording medium, when preparing a magnetic layer forming liquid by dispersing magnetic particles in a resin solution (9 inder solution), the dispersibility of the magnetic particles in the inder is determined. In order to obtain a good result, a surfactant is generally added to the magnetic layer forming liquid as a dispersant.

The surfactants commonly used here include higher fatty acids, sanctioned aliphatic alcohols, phosphate esters, etc., and by adding these to the magnetic layer forming solution, the However, on the other hand, these conventionally used surfactants have poor binding properties with their own inders, so it is difficult to manufacture them. over time from the surface of the magnetic layer of a magnetic recording medium.

This causes a phenomenon of oozing out (migration), and as a result, it has the defect that a good quality magnetic layer cannot be maintained for a long period of time.

Purpose The present invention provides a magnetic recording medium that eliminates the above defects and maintains high quality performance over a long period of time.

In order to achieve such an objective, the present inventor has conducted a lot of research and consideration on various dispersants and magnetic recording media, and has found that if a specific dispersant is used, the dispersant will chemically bond with the binder. It has been found that the particles are bound together, exhibit sufficient dispersibility, and do not cause any oozing phenomenon to the surface of the magnetic layer. The present invention was completed based on this knowledge.

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of magnetic particles and a binder is provided on a non-magnetic support, in which the magnetic layer has the following general formula (where 几 is hydrogen or a methyl group, and n is 1 or an integer of 2) is added.

To explain the present invention in more detail below, the nonmagnetic support in the magnetic recording medium of the present invention includes resin films such as polyethylene terephthalate, polypropylene, cellulose triacetate, cellulose diacetate, and polyimide, synthetic paper, and aluminum foil. I can give an example.

As magnetic particles, y -Fe1O@, Fe@04,
co-containing r” Fe1O,1, Co-containing Fe104,
Typical examples include Oo adhesion r -Pe5o@.

The binder is not particularly limited as long as it is commonly used in this field, but preferably an electron beam curable binder is used. This is due to the adoption of a magnetic recording media manufacturing method that uses an electron beam curable inder to form the magnetic layer, which prevents the solid content in the magnetic paint (magnetic layer forming liquid) from coagulating and reduces the pot life. This is because it is considered to be advantageous in terms of improvement, simplification of the manufacturing process, energy saving, etc. A combination of electron beam curable glue and a thermosetting binder can also be used effectively.

Typical examples of the electron beam curable compounds include oligomers or prepolymers having ester skeletons, ether skeletons, urethane skeletons, epoxy skeletons, etc. having acrylic double bonds, such as urethane acrylate oligomers, polyester/acrylate polymers, etc. polymers, polyether/acrylate prepolymers, epoxy/acrylate pre-I remers, polyester/urethane/acrylate prepolymers, and the like. Examples of the thermosetting resin include urethane resins, epoxy resins, cellulose resins, and mixtures of these with vinyl chloride resins, dinylidene chloride resins, and the like.

In order to form the magnetic layer on the support, as mentioned above,
It is necessary to prepare a magnetic layer forming liquid, and examples of solvents used for this purpose include acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, toluene, xylene, hexane, and heptane.

This magnetic layer forming liquid must contain at least one dispersant represented by the above general formula.

The amount of dispersant added here is 1 to 10
]ti% is appropriate.

If the amount added is less than 1% by weight, the effect as a dispersant cannot be fully exhibited, and conversely, if the amount added is more than 10% by weight, the magnetic particles occupy less than the amount of the magnetic layer formed in the unit volume. The amount of body is reduced, which is unfavorable in terms of magnetic properties.

The compounds represented by the above general formula are specifically the following four, and these compounds are, for example, MR-200 (mixture of compound 41 and fu 2) manufactured by Daito Kogyosei Co., Ltd.
Alternatively, it can be obtained under the trade name AR-200 (mixture of compounds /163 and /I64) manufactured by Daito Kogyo Seisei.

It is desirable to add appropriate additives, such as antistatic agents, lubricants, and abrasives, to the magnetic layer in addition to the magnetic particles, inders, and dispersants mentioned above.

As the antistatic agent, conductive fine powder such as carbon black, graphite, carbon black graft, mer, etc. is used. When adding these antistatic agents,
The amount thereof is preferably 10 parts by weight or less, preferably 3 to 10 parts by weight, per 100 parts by weight of the magnetic particles.

As a lubricant, silicone oil, di(iiffed molydimolybdenum ~C2° basic fatty acid and C,~011
Fatty acid esters consisting of m alcohols and the like are used. When adding these lubricants, the amount should be 10 parts by weight or less, preferably 3 parts by weight per 100 parts by weight of the magnetic particles.
~10 parts by weight.

An abrasive may also be added if necessary, but in an appropriate amount.

To actually produce the magnetic recording medium of the present invention, magnetic particles,
A binder and a specific dispersant (at least one of those represented by the general formula) are essential components, and the above-mentioned additives are appropriately added to the binder and dispersed or dissolved in a solvent to prepare a magnetic layer forming liquid. After coating on a non-magnetic support with a doctor blade or other means, it is heated and dried to remove the weft agent, and then irradiated with an electron beam to harden the p%+1 ingu to form a magnetic film with a thickness of 2 to xopm. What is necessary is to form a layer.

The amount of magnetic particles occupying the entire magnetic layer is 50 to 70% by weight. Further, when a compound other than the compound represented by the above general formula is used as a dispersant, it is desirable to limit the amount to 50% by weight or less based on the total amount of the dispersant.

Example I Co-containing -FetO, 100 parts by weight Phosphate ester compound (AR-200, manufactured by Daihachi Kogyo Co., Ltd.) 4 parts by weight Vinyl chloride-vinyl acetate copolymer (VAGH, manufactured by UOC) 20 parts by weight Urethane acrylate oligomer (M-1200X.

Shokua Gosei Kagaku Kogyo Gen Co., Ltd. 20 parts by weight Methyl ethyl ketone 100x parts Cyclohexanone 100 parts by weight □
After dispersing the mixture in a ball mill for 48 hours, approximately 3
It was filtered through a 75 μm thick polyester film using a 1 mil doctor blade and dried at 100°C to remove the solvent.
An absorbed dose (electron beam) of 0 KV - 10 Mrad was irradiated to harden the inder to form a magnetic layer with a thickness of about 3 μm, thereby producing 8 magnetic recording media (Product 1 of the present invention).

Example 2 A magnetic recording medium (invention product 2) was produced in the same manner as in Example 1 except that the phosphoric acid ester compound -HMR-2oo (manufactured by Daihachi Kogyosho Co., Ltd.) was used instead.

Comparative Example 1 A magnetic recording medium (comparative product 1) was produced in exactly the same manner as in Example 1, except that 4 parts by weight of lecithin was used instead of the 4N phosphoric acid ester compound (AR-200).

Comparative Example 2 A magnetic recording medium (comparative product 2) was produced in exactly the same manner as in Example 1, except that 2 parts by weight of lecithin was used instead of 4 parts by weight of the phosphoric acid ester compound (AR-Zoo).

The magnetic properties of these four types of samples were measured, and the presence or absence of bleeding of the dispersant onto the surface of the magnetic layer (presence or absence of migration) was observed. In addition, to observe the presence or absence of migration, the sample was placed at 50°C and 80% RJ for 4 hours.
After leaving it for 8 hours, it was taken using an electron microscope (photo magnification: 2).
000 times)). The results were as shown in Table-1.

Table 1 As is clear from the above test results, the magnetic recording medium according to the present invention can fully achieve its purpose.

This is because the compound (dispersant) represented by the above general formula has an acrylic double bond at the end, so the reaction does not proceed at the stage of magnetic dye dispersion (magnetic layer forming liquid). When this magnetic layer forming liquid is applied onto a non-magnetic support, heated and dried, and further irradiated with an electron beam, the double bond radically polymerizes with the double bond of the non-inder component.
This is thought to be because migration of the dispersant to the surface of the magnetic layer is prevented.

Claims (1)

[Scope of Claims] t A magnetic layer mainly composed of magnetic particles and a nonmagnetic inder is provided on a nonmagnetic support, and the magnetic layer contains the following general formula (where R is hydrogen or A magnetic recording medium characterized in that it contains a dispersant represented by the following: methyl group, n is an integer of 1 or 2.