JPH01282726A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having excellent durability and dispersibility by using polyurethane having a mercapto group as a polar group in the molecule as a binder to constitute a magnetic layer. CONSTITUTION:This recording medium has the magnetic layer essentially consisting of ferromagnetic powder and binder on a nonmagnetic base and the binder contains the polyurethane having the mercapto group in the molecule. Namely, the polyurethane has the mercapto group. The dispersibility of the magnetic powder is thereby improved and the magnetic characteristics and electromagnetic conversion characteristics (frequency characteristic, S/N and C/N) are improved. The magnetic powder is securely bonded by the binder and the mercapto group and, therefore, the desorption of the magnetic powder is decreased and the level fluctuation, output attenuation and the degradation in the durability of the medium by powder dislodgment such as clogging are extremely lessened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly to a binder contained in a magnetic layer formed on a non-magnetic support. This is related to the improvement of.

[Summary of the invention]

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, in which the binder constituting the magnetic layer has a mercapto group as a polar group in the molecule. By using polyurethane having the following properties, it is intended to provide a magnetic recording medium with excellent durability and dispersibility.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Polyurethane or polyester is widely used as a binder for magnetic recording media because of its good abrasion resistance and durability of the magnetic layer. However, conventional polyurethane and polyester have been insufficient in terms of affinity and dispersibility with magnetic powder.

In addition, polyurethanes and polyesters containing 10H5 in the molecule, although the above-mentioned affinity and dispersibility were slightly improved, were still not sufficient.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned disadvantages, and to provide a magnetic recording medium that has extremely good dispersibility for magnetic powder and excellent durability in terms of dust removal and still characteristics.

[Means to solve the problem]

The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic layer mainly composed of ferromagnetic powder and a binder on a non-uniform support, wherein the binder contains polyurethane having a mercapto group in the molecule. It is characterized by:

According to the invention, the polyurethane has mercapto groups. Therefore, this mercapto group improves the dispersibility of the magnetic powder, and the magnetic properties and electromagnetic conversion properties (frequency properties, S
/N, C/N) is improved, and because the magnetic powder is strongly bonded to the binder by the mercapto group, there is less detachment of the magnetic powder, which reduces powder drop-off such as level fluctuation, output attenuation, black nogging, etc. The durability of the media due to this is significantly improved.

In the present invention, the content of mercapto groups is preferably 0.005 to 1.0 mmol/g based on the polyurethane. The first reason is that if it is less than 0.005 m mol/g, there is little effect on dispersibility;
This is because if it exceeds mol/g, the solubility in the solvent decreases and the moisture resistance of the resulting coating film also deteriorates.

Further, the number average molecular weight of the polyurethane containing a mercapto group is preferably 5,000 to 100,000.

If this molecular weight is less than 5,000, durability is insufficient, and 1
If it exceeds 00.000, solubility in solvents will decrease.

The polyurethane having a mercapto group in the molecule of the present invention is not particularly limited as long as it is produced by applying a generally known method for introducing a mercapto group.

As a method for introducing mercapto groups into polyurethane,
For example, in the case of polyester polyurethane, there are the following methods.

First, a polyester having a mercapto group is synthesized, and then the obtained polyester is subjected to a urethanization reaction.

Here, when synthesizing polyester, isophthalic acid, terephthalic acid, adipic acid, etc. are used as acid components, while ethylene glycol, 1.4-
Butylene glycol, 1゜6-hexylene glycol,
Use neopentyl glycol, etc. As part of the acid component or glycol component, for example, 3-mercapto-1,2-propanediol, 1,4-dimercapto-2,3-butanediol, or thiomalic acid may be used.

In addition, in the urethanization reaction, the polyester containing a mercapto group and the polyester not containing a mercapto group obtained as described above were used as the polyol component, and as the isocyanate, 4゜4-diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate was used. etc. as a chain extender using 1.
4-butylene glycol, neopentyl glycol, ethylene glycol, 1,6-hexylene glycol, etc. are used.

The above-mentioned mercapto group-containing polyurethane may be used in combination with other binders.

As such other binders, those conventionally used as binders for magnetic recording media can be used, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, Vinyl chloride-vinylacetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer , polyvinyl butyral, cellulose derivatives, styrene-butadiene copolymers, polyesters, phenol resins, epoxy resins, thermosetting polyurethanes, urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof.

Among these, polyurethane, polyester, acrylonitrile butadiene copolymer, etc., which are said to impart flexibility, are preferred.

A hydrophilic polar group may be introduced into the mercapto group-containing polyurethane or other binder used in combination for the purpose of further improving dispersibility.

The hydrophilic polar groups include -5O3FX group, -050
3M also (, -PO(OM')z group, -C00M group, -
NG, J group (where M represents a hydrogen atom or an alkali metal atom, M' represents a hydrogen atom, an alkali metal atom or a hydrocarbon atom, G represents an alkyl group, and J represents a halogen, respectively.

) etc.

In the magnetic recording medium of the present invention, the magnetic layer is formed by coating the surface of the non-magnetic support with a magnetic paint prepared by, for example, dispersing ferromagnetic powder in the above-mentioned binder and dissolving it in an organic solvent.

Here, the material of the non-magnetic support may be any material that is normally used in this type of magnetic recording medium, such as polyesters such as polyethylene terephthalate, polyolefins such as polyethylene, polypropylene, etc. cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide, and polyamideimide;
Examples include paper, aluminum, copper, and other light alloys, aluminum alloys, titanium alloys, and other light alloys, ceramics, single crystal silicon, and the like. The nonmagnetic support may be in any form such as a filter, tape, sheet, disk, card, or drum.

Moreover, any ordinary ferromagnetic powder can be used as the ferromagnetic powder used in the magnetic layer. Therefore, ferromagnetic powders that can be used include ferromagnetic iron oxide particles,
Examples include ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite i particles, iron nitride, and the like.

The above-mentioned ferromagnetic iron oxide particles are those whose value of X is in the range of 1.33≦X≦1.50 when expressed by the general formula FeOx, that is, maghemite (T-Pez03, x = 1.50).
50) ,? Gnetite (Fe304, x = 1.33
) and their solid solutions (FeOx, 1.33<x<
1.50).

Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide may include CrO□ or Ru, Sn, Te for the purpose of improving coercive force.
, Sb, Fe, Ti, , V, Mn, etc. can be used.

Ferromagnetic alloy powders include Fe, Co, Ni, F
e-Co, Fe-Ni, Fe-Co-Ni, Co-
Ni, Fe-Co-8% Fe-Co-Cr-
B, Mn-B1. Mn-82, Fe-Co-V, etc. can be used, and for the purpose of improving various properties of these, 811, Si, , Ti, CrXMn5 Cu, Z
A metal component such as n may be added.

In addition to the binder and ferromagnetic powder, the magnetic layer also contains additives such as a dispersant, a lubricant, an abrasive, an antistatic agent,
A rust preventive agent or the like may be added. These dispersants, lubricants,
Any conventionally known abrasives, antistatic agents, and rust preventives can be used.

The constituent materials of the magnetic layer described above are prepared as a magnetic paint by dissolving it in an organic solvent and applied onto a non-magnetic support.The solvent for the magnetic paint may be acetone, methyl ethyl ketone, methyl isobutyl getone, cyclohexanone, etc. Ketone solvents, methyl acetate, ethyl acetate, butyl acetate,
Ester solvents such as ethyl lactate and glycol monoethyl acetate, glycol ether solvents such as glycol dimethyl ether, glycol monoethyl ether, and dioxane, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and fats such as hexane and heptane. Group hydrocarbon solvents, methylene chloride, ethylene chloride,
Carbon tetrachloride, chloroform, ethylene chlorohydrin,
Examples include organic chlorine compound solvents such as dichlorobenzene.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Joshin 1 Wani ΣAkira Co coated r-Fe203 100 parts by weight (specific surface area 40 m/g) Norcapto group-containing polyurethane 10 parts by weight Carbon black (antistatic agent) 2 parts by weight Crzl
l) + (abrasive) 2 parts by weight stearic acid (lubricant) 1 part by weight butyl stearate (lubricant) 1 part by weight methyl ethyl ketone 150 parts by weight toluene 150 parts by weight cyclohexanone 60 parts by weight The above composition was milled in a ball mill. After mixing for 24 hours and subsequently adding 4 parts by weight of Sumidur L (trade name, manufactured by Jusman Bayer Urethane GmbH) as a curing agent, after 30 minutes, filtering through a 3 μm filter, this was mixed with 14 μm thick polyethylene terephthalate. The film was coated so that the thickness of 119 after drying was 6 μm. Next, after performing a magnetic field orientation treatment, it was dried and wound up. After further supercalendering, heat treatment was performed at 75°C for 24 hours, and 1/2
Sample tape cut into 2 inch width (Examples 1 to 6)
I created ゛.

The mercapto group-containing polyurethane used was obtained by synthesis, and its number average molecular weight and amount of mercapto group introduced (m mol/g) are shown in the table.

For each sample tape obtained, gloss,
R3, still characteristics, and drop-off were measured.

In addition, the above still characteristics are 4.2Mtl on the sample tape.
The video signal of z was recorded, and the time until the playback output attenuated to 50% was taken as the time. Also, powder removal takes 60 minutes by shuttle 100.
After running twice, the amount of powder falling onto the head drum, guide, etc. was visually observed and evaluated using a point deduction method (-5 to 0).

The results are shown in the table.

Sample tapes were prepared in the same manner as in Examples 1 to 6, except that polyurethane having no mercapto group was used in place of the mercapto group-containing polyurethane in Examples 1 to 6, and evaluated in the same manner. The results are shown in the table.

(Left below) [Effects of the Invention] As detailed above, in the magnetic recording medium of the present invention, by using a mercapto group-containing polyurethane as a binder, the dispersibility of magnetic powder is significantly improved, and powder drop-off and Since it has extremely excellent durability such as still characteristics, it is extremely useful as a magnetic tape, for example, and has great industrial value.

Claims (1)

[Claims] A magnetic recording medium having a magnetic layer mainly composed of ferromagnetic powder and a binder on a non-magnetic support, wherein the binder contains polyurethane having a mercapto group in its molecule.