JPS60121524A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To disperse uniformly magnetic powder into a binder and to obtain a magnetic recording medium having an excellent magnetic characteristic by coating the magnetic powder with a specific material. CONSTITUTION:Magnetic powder is successively coated with polyisocyanate and a resin having a functional group that can react with the isocyanate group with a magnetic recording medium provided with a magnetic layer consisting essentially of the magnetic powder and resin binder on a nonmagnetic base. Manufacture of the coated magnetic powder is accomplished by adding first a soln. of polyisocyanate to the magnetic powder while agitating the powder in a kneader under the reduced pressure. The mixture is agitated and kneaded for substantial time (about >=15min) at an ordinary temp. or if necessary, at about 50-90 deg.C. A soln. of the resin is thereafter added and the satisfactory coated powder is obtd. if the powder mixture is kept agitated and kneaded for substantial time (about >=30min) at about 50-90 deg.C. The coated magnetic powder obtd. in such a way is cleaned and refined by a solvent for the polyisocyanate and the resin if necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a magnetic recording medium used as a magnetic tape, magnetic flexible disk, or the like.

PRIOR TECHNOLOGY Conventional magnetic recording media mainly consist of magnetic powder such as iron fluoride or chromic acid and a binding agent made of various thermoplastic resins, thermosetting resins, or reactive resins on a non-magnetic support such as a plastic film. A magnetic layer is provided as a component. In order to obtain good magnetic properties in such a magnetic recording medium, it is necessary to use as fine a magnetic powder as possible and to uniformly disperse it in the magnetic layer. For this reason, in the past, surfactants such as lecithin, higher fatty acids, phosphoric esters, higher alcohols, and diamine salts were added to the magnetic layer as dispersants for the magnetic powder, or in order to improve the dispersibility of the magnetic powder itself,
Magnetic powder coated with a coupling agent such as silane, titanium, or aluminum has been used. However, conventional dispersants or dispersion coating agents are insufficiently effective, and have the disadvantage that the finer the magnetic powder, the lower the dispersibility.

Object The object of the present invention is to provide a magnetic recording medium in which fine magnetic powder is uniformly dispersed in a binder, and therefore has excellent magnetic properties.

Structure The magnetic recording medium of the present invention is a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a resin binder is provided on a non-magnetic support, in which the magnetic powder has a functional layer capable of reacting with /isocyanate and incyanate groups. It is characterized by being sequentially coated with resins having groups.

It is believed that the dispersion effect of the dispersant or dispersion coating agent on the magnetic powder depends on the bonding force between these materials. However, in conventional magnetic recording media, this bonding force is based on the adsorption force between the materials and is therefore relatively weak. On the other hand, since the magnetic recording medium of the present invention utilizes the reactivity between materials,
This binding force is strong, and therefore the dispersion effect is also large.

That is, in the case of the present invention, a polyinocyanate that is reactive with the magnetic powder itself is used as a base, and the surface of the magnetic powder is coated with a uniform and strong bond due to its reactivity, and then a resin that is reactive with isocyanate groups is applied on top of that. It is used as a dispersion coating material to provide a uniform and strong bonding coating due to its reactivity.

K for making the coated magnetic powder used in the present invention is generally firstly
While stirring the magnetic powder in a kneader under reduced pressure, the polyisocyanate solution is added dropwise, sprayed, etc. to cause an addition reaction, and the reaction is completed and simultaneously dried at ~ room temperature or as necessary. After stirring and kneading for a sufficient time (about 15 minutes or more) at a temperature of about 50 to 9 OC, the solution of the above-mentioned xyt resin is added and reacted in the same manner as described above, and then dried at the same time as the reaction is completely completed. In order to do this, stirring and kneading may be continued for a sufficient time (about 30 minutes or more) at a temperature of about 50 to 90C. Next, since excess or unreacted yIe linocyanate and/or the resin may be attached to the surface of the coated magnetic powder thus obtained, it is necessary to remove the coated magnetic powder t- Washing and purification with a polyisocyanate and a solvent for the resin.

Note that the concentration of each solution of the polyisocyanate and the resin is preferably as low as 1% by weight or less in order to perform a uniform reaction. The amount of polyinocyanate and the resin used is preferably 1 to 10% and 1 to 15%, respectively, based on the magnetic powder. If each is below the lower limit, it is difficult to obtain the desired effect, and if it is above the upper limit, it may be excessive as a reaction component. Yes, it is uneconomical.

Polyisocyanates used as primers include diphenylmethane diisocyanate, toluene diisocyanate,
Bifunctional incyanates such as hexamethylene diisocyanate, dicyclohexylmethane diinocyanate, and inphorone diisocyanate, trifunctional incyanates such as triphenyl meta/triinocyanate, and polyisocyanate adducts and blocked isocyanates synthesized from these. , Polymerized polyisocyanate (commercially available product is Koro$- manufactured by Nippon Boliure 1'7)1. , same■L
; Desmodur L manufactured by Tumainil; and Azizolene LD-213 manufactured by DuPont. ) can be exemplified. Any resin can be used as a dispersant as long as it has a functional group that can react with an isocyanate group, such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer, commercially available products such as WAG)t manufactured by UCC, and VYNC. There is.

), vinyl chloride-vinyl acetate copolymer (e.g. VYH■ manufactured by UCC), polyurethane resin (e.g. Epicoat manufactured by Shell Chemical Co.), polyurethane resin, phenoxy resin (e.g. PKHH manufactured by UCC), polyvinyl butyl , Poly♂ Nirhor! Examples include polyester resin (for example, d-iron resin manufactured by Toyobo Co., Ltd.), nitrocellulose, and the like. The magnetic powder coated with the above materials is r-F*@Om t Fe2O2e.
Co-containing "10 m e Co coating - FslO@t
A ferromagnetic alloy composed of at least two of Co-containing Fe104, Co, Fs, Ni, etc. can be used. Ethyl acetate, xylene, methyl ethyl ketone, toluene, dimethylformamide, tetrahydrofuran, etc. are used alone or in combination as solvents for polyisocyanates and for resins having functional groups capable of reacting with incyanate groups.

As the binder used in the magnetic layer, common thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. As thermoplastic resins, for example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic ester styrene Copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane distomer, polyginyl fluoride, chloride-disdene acrylonitrile copolymer, pig Gen-acrylonitrile copolymer, polyamide resin, polyvinyl butyl, cellulose derivative, styrene-citadiene copolymer, polyester resin,
Amino resins, various synthetic rubber-based thermoplastic resins (polyzotadie, roloprene, polyisoprene, styrene-citadiene copolymers, etc.), and mixtures thereof are used. Emulsions of these are also used.

Examples of thermosetting resins or reactive resins include phenol-formalin-resol resin, phenol-formalin-resole resin, phenol-formaldehyde resin, xylene-formaldehyde resin, urea resin, melamine resin, and drying oil-modified resin. Alkyd resin, phenolic resin-modified alkyd resin, maleic acid resin-modified alkyd resin ~ unsaturated polyester resin, epoxy resin and curing agent (polyamine, acid anhydride, polyamide resin, etc.), terminal isocyanate polyester moisture-curing resin, terminal incyanate These include polyether moisture-curable resins, polyisocyanate prepolymers, resins containing polyisocyanate prepolymers and active hydrogen, and mixtures thereof. Emulsions of these are also used.

These binders may be used alone or in combination;
Other additives may be added. The amount of binder in each magnetic layer is in the range of 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the coated magnetic powder.

In addition to the binder and coated magnetic powder, additives such as a lubricant, abrasive, and antistatic agent may be added to each magnetic layer.

Antistatic agents include Carin Black, Gutuphite,
Conductive fine powder such as Carne Black graft polymer; Natural surfactants such as saponin; Nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts, pyridine, and other Cationic/surfactants such as heterocycles, phosphoniums or sulfoniums; carmenic acid,
Anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols are used.

As lubricants, conductive fine powders such as carmenzo2, gutphite, and carzen black graft polymers; inorganic fine powders such as molybdenum disulfide and tungsten disulfide; polyethylene, polypropylene, ethylene♂nyl chloride copolymers, and Plastic fine powder such as tetrafluoroethylene; α-olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at room temperature (a compound in which an n-olefin double bond is bonded to the terminal carbon, carbon number 20); carbon number 12 ~2
Fatty acid esters consisting of 0 monobasic fatty acids and monohydric alcohols having 3 to 12 carbon atoms can be used.

Commonly used abrasive materials include fused alumina,
Silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, Zaku Shiho, emery (main components: corundum and magnetite), etc. are used. These abrasives have a Mohs hardness of 5 or more and an average particle diameter of 0.05 to 5 μm, particularly preferably 0.1 to 2 μm.

Non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as one-stroke V acetate, paper, synthetic paper, films such as aluminum, and their like. Complexes etc. are used.

To make the magnetic recording medium of the present invention, coated magnetic powder, a binder, and various additives if necessary are dissolved or dispersed in a suitable solvent, and the resulting magnetic coating is coated on a non-magnetic support and dried. If necessary, perform heat treatment to harden the coating film to a thickness of 1
A magnetic layer having a thickness of about 5 μm may be formed. In addition, as a solvent, acetone, methyl ethyl ketone, cyclohexanone,
Xylene, hexane, etc. are used.

Effect As described above, when the surface of the magnetic powder is coated with polyisocyanate and a resin having a functional group that can react with the incyanate group, the polyisocyanate and the resin are sequentially coated on the magnetic powder due to the reactivity of these materials. As a result of uniform bonding, the dispersibility of the magnetic powder in the binder is significantly improved, resulting in a magnetic recording medium with excellent magnetic properties.

Examples of the present invention are shown below. Note that all parts are parts by weight.

Example 1 100 parts of Co-coated r-Fe, O@ (coercive force He = 640 Oe, particle size 0.3μ) were placed in a kneader,
While stirring under reduced pressure, 3 parts of a 1% ethyl acetate solution of toluene diisocyanate was sprayed onto the surface of the j-F@101 using a spray gun. After further stirring and kneading for about 15 minutes, polyester resin (manufactured by Toyobo Co., Ltd.) 9 In the same manner, 5 parts of an ethyl acetate solution of 300) was sprayed, followed by stirring and mixing at 50 U for about 30 minutes.The resulting powder was washed with ethyl acetate, dried, and the surface was coated with toluene diisocyanate and Co coated r − sequentially coated with polyester resin
F * 10g (1) t" was obtained. Next, a liquid with a recipe consisting of 100 parts dimethylformamide 150 parts methyl ethyl lactate 7 150 parts was dispersed in a Zeel mill for 30 hours. This t-75μ thick ester film was coated with a blade to a dry thickness of 3μ, and dried to form a magnetic layer to produce a magnetic recording medium.

Example 2 A 1% ethyl acetate solution of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by UCC) was used instead of a 1% ethyl acetate solution of polyester resin during production of coated magnetic powder. Co-coated r-F, whose surface was sequentially coated with toluene diisocyanate and vinyl chloride-vinyl acetate-vinyl alcohol copolymer using the same method as in Example 1.
tos (2) t″ was obtained.Hereinafter, this coating r −F
A magnetic recording medium was produced in the same manner as in Example 1 using @SoOn (2).

Example 3 During the production of coated magnetic powder, a 1% ethyl acetate solution of polyester resin (Epicor 0L-53-B-40, manufactured by Shell Chemical Co., Ltd.) was used instead of a 1% ethyl acetate solution. Co-adhered y-F* whose surface was coated with toluene diincyanate and epoxy resin in the same manner as in Example 1
10B(3)c was obtained.

Hereinafter, a magnetic recording medium bar was prepared in the same manner as in Example 1 using this substrate 11 r -F@lO,(3)@.

Comparative Example 1 Example 1 except that 0.100 parts of untreated Co-deposited r-F. and 3 parts of lecithin were used as a dispersant instead of 100 parts of N1co-deposited r-F@10s (1). A magnetic recording medium was created using the same method.

Comparative Example 2 Coated Co coating 1-F, O, (13100 parts 0 fl A magnetic recording medium was created using this method.

Next, the magnetic properties and dispersibility of the magnetic powder were investigated for the above magnetic recording media, and the results shown in the table below were obtained.

*It is expressed as Br/Bm' (Br: residual magnetic flux density, Brl saturation magnetic flux density), and the larger this value, the better the dispersibility.

This table shows that when the surface of the magnetic powder is coated with i-/linocyanate and a resin reactive with it as in the present invention, a magnetic recording medium with good dispersion of the magnetic powder and excellent magnetic properties can be obtained. I understand O

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a resin binder is provided on a non-magnetic support, the magnetic powder is sequentially coated with polyisocyanate and a resin having a functional group that can react with incyanate groups. A magnetic recording medium characterized by: