JPH01251316A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability by using ferromagnetic powder having a specific surface area and a specific hardener. CONSTITUTION:The ferromagnetic powder having >=45m<2>/g specific surface are measured by a BET method is used as the ferromagnetic powder constituting the magnetic layer on a nonmagnetic base. Fe, Fe-Co, Fe-Co-Ni, etc., or acicular metal powders contg. slight ratios of additive elements such as Al, Cr and Si by taking corrosion resistance or prevention of sintering at the time of production, etc., into consideration are used for the ferromagnetic powder. The binder is cured by the aliphat. hardener and/or alicyclic hardener. The binder includes the binders formed by introducing polar groups into, for example, a polyester resin, polyurethane resin and vinyl chloride resin. The durability is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium with significantly improved durability.

[Summary of the invention]

The magnetic recording medium of the present invention uses a ferromagnetic powder having a specific specific surface area and a specific hardening agent, thereby achieving
This has significantly improved durability.

[Conventional technology]

Conventionally, to improve the durability of magnetic recording media, aromatic isocyanate (TDI) curing agents, such as Coronat (trade name, manufactured by Nippon Polyurethane Co., Ltd., TDI curing agent), which react with hydroxyl groups in the binder, have been used. It's here. Since coronate is a trifunctional isocyanate compound, it reacts with the side chains and terminal hydroxyl groups of the binder, making it possible to create a three-dimensional network structure.

[Problem to be solved by the invention]

However, TDI hardeners such as Coronate L are highly reactive and may react not only with the binder and hydroxyl groups, but also with moisture in the paint and water adsorbed on the surface of the magnetic powder. If the isocyanate groups of the curing agent react with water before the hydroxyl groups of the binder, the number of effective isocyanate groups that react with the hydroxyl groups of the binder will decrease, making it impossible to create three-dimensional crosslinks. .

Moreover, the above-mentioned phenomenon was particularly microscopic in Co-adhered 1-Peso and metal magnetic powder having a specific surface area of 45 m/g or more.

An object of the present invention is to eliminate the above-mentioned disadvantages and to provide a magnetic recording medium with significantly improved durability.

[Means to solve the problem]

The magnetic recording medium of the present invention has a magnetic layer mainly composed of ferromagnetic powder and a binder on a non-magnetic support, wherein the ferromagnetic powder has a specific surface area of 45 m"/g or more, Further, the binder is cured with an aliphatic curing agent and/or an alicyclic curing agent.

In the present invention, as described above, the ferromagnetic powder constituting the magnetic layer has a specific surface area of 45 rrr/g or more as measured by the BET method. This has a specific surface area of 45rrr
This is because particles with a particle size of /g or less can be expected to be more effective in improving the S/N. Further, when modulation noise is measured, it has been found that when the specific surface area is set to 45rd/g or more, a desired low noise level can be achieved even at a short recording wavelength of 1 μm or less. This specific surface area is 45n? /g or more as long as it does not become superparamagnetic, but as a practical matter, it is 45 to 150 i/g.
g is preferred.

The ferromagnetic powder used in the present invention is Fes Fe-Co
, Pe-Co-Ni, etc., or for example, considering corrosion resistance or sintering prevention during manufacturing, etc., 8l% Crs S
Acicular metal powder containing lft additive elements such as t can be used. These acicular metal powders are prepared by using acicular iron oxide, hydrated iron oxide, N5. C
It can be obtained by reducing iron oxide or hydrated iron oxide containing metals such as o in a reducing atmosphere such as H2 gas. Note that the specific surface area of this ferromagnetic powder can be controlled by selecting the specific surface area of these above-mentioned starting materials.

Examples of the binder used in the present invention include polyester resins, polyurethane resins, and vinyl chloride resins into which polar groups have been introduced. These resins can be obtained by various methods. For example, a sulfonate metal base-containing polyester resin can be obtained by using a dicarboxylic acid containing a sulfonate metal base as part of the dicarboxylic acid component, and condensing this with a dicarboxylic acid not having a sulfonate metal base together with a diol. can. Polyurethane resins containing sulfonate metal bases can be obtained by condensation and addition reactions using the three starting materials of the above-mentioned sulfonate metal base-containing polyesters together with diisocyanates.

Furthermore, a method of modifying polyester resin, polyurethane resin, or vinyl chloride resin to introduce polar groups may be considered. That is, these resins and, for example, Cl-CIIzCHzS (hM, CI CHzCll
zO3Off? ! .

(oMz) Cj! CHz COOH, CI CHz -P
This is a method of condensing and introducing the above polar group and a compound containing chlorine into a molecule such as (OM+) by a dehydrochloric acid reaction.

The carboxylic acid components used in this invention to obtain polyester resins and polyurethane resins include terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-
Aromatic dicarboxylic acids such as naphthalic acid, aromatic oxycarboxylic acids such as p-oxybenzoic acid and p-(hydroxyethoxy)benzoic acid, aliphatic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. Examples include dicarboxylic acids, tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid. Particularly preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid.

Examples of the dicarboxylic acid component containing a sulfonic acid metal group include 5-sodium sulfoneisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

Diol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-bentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2 ,2.4-1
-dimethyl-1,3-bentanediol, 1,4-cyclohexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol, ethylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and so on. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination.

The diisocyanate components used in this invention to obtain the polyurethane resin include 2.4-tolylene diisocyanate, 2.6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate,
Hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4°4'-biphenylene diisocyanate, 4.4' -diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,3-naphthalene diisocyanate, p
-xylylene diisocyanate, m-xylylene diisocyanate, 1.3-diisocyanatemethylcyclohexane, 1.4-diisocyanatemethylcyclohexane, 4.4''-diisocyanatedicyclohexane, 4
．． Examples include 4'-diisocyanate dicyclohexylmethane and isophorone diisocyanate. .

When modifying vinyl chloride resin to introduce a sulfonic acid metal base, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, chloride Vinyl-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer, etc. are used.

And the OH of vinyl alcohol contained in these
and CE CtlzCIIzS (hM, CI
With chlorine of sulfonic acid metal salt containing chlorine such as SOJ,
A method of dehydrochlorination reaction can be used in a polar solvent such as dimethylformamide or dimethyl sulfoxide in the presence of a dehydrochlorination agent such as an amine such as pyridine, picoline, or triethylamine, or an epoxy compound such as ethylene oxide or propylene oxide. .

In this invention, the molecular weight of the binder is preferably 50,000 or less. This is because if the molecular weight exceeds 50,000, the viscosity of the paint will exceed the allowable range when the specific surface area of the magnetic powder is increased by the BET method. The molecular weight of the binder is 2.0
00 or more is preferable. This is because if the above molecular weight is less than 2,000, unreacted components will be generated when the magnetic paint is applied onto the support and then cured using a curing agent, and low molecular weight components will remain, causing the coating film to deteriorate. This is because it deteriorates physical properties.

Further, in the present invention, the binder containing a polar group preferably has a molecular weight per polar group of 200 to 50,000. This is because if it is less than 200, the hydrophilicity of the resin will be too strong, resulting in poor solubility in solvents, compatibility with other resins in the binder, and moisture resistance of the magnetic layer. , ooo or more, the effect on dispersibility will be insufficient.

Furthermore, the weight ratio P/B of the ferromagnetic powder and the binder constituting this magnetic layer is selected to be 3 to 12, preferably 4 to 8. This is because if the amount of binder is too large, that is, if P/B is too small, the residual magnetic flux density Br will be insufficient and S/
This is because if the improvement in N is not achieved and P/B is too large, powder dropout increases and magnetic resistance deteriorates.

The curing agent used in the present invention may be an aliphatic curing agent and/or an alicyclic curing agent. This aliphatic curing agent may be any commonly known one, such as hexamethylene diisocyanate (HD■), trimethylhexamethylene diisocyanate (TMDI), Coronate EH (trade name, Manufactured by Nippon Polyurethane Co., Ltd., HDI series) Coronet 1-HL (product name,
Manufactured by Nippon Polyurethane Co., Ltd., HDI series), Takenate D-1
7ON (trade name, manufactured by Narita Pharmaceutical Co., Ltd., HDI series) is mentioned. Further, the alicyclic curing agent may be any one that is generally known, such as isophorone diisocyanate (IPDI), bis(isocyanate methyl)cyclohexane (HXDI), and takenate D-14ON ( (trade name, manufactured by Narita Pharmaceutical Co., Ltd., IPDI series). Among these, it is preferable to use Coronate EH and Coronate 1-HL as aliphatic hardeners, and Takene 1-D-14ON as alicyclic hardeners. These may be used alone or in a mixed system.

The blending ratio of this curing agent is usually 5 to 50 parts by weight based on 100 parts by weight of the total binder. If this blending ratio is less than 5 parts by weight, crosslinking properties will be insufficient, durability will be poor, and 50 parts by weight will result.
If the amount exceeds the weight part, the paint properties will deteriorate. Preferably 10
~40 parts by weight.

Furthermore, it is possible to add aluminum oxide, chromium oxide, or silicon oxide as reinforcing agents to the magnetic layer, as well as olive oil as a lubricant, carbon black as an antistatic agent, and lecithin as a dispersant.

A magnetic paint is prepared by dissolving the constituent materials of the magnetic layer in an organic solvent, and this is applied onto a non-magnetic base. ), alcohols (e.g. methanol,
ethanol, propatool, butanol), esters (e.g. methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate, monoethyl ether), glycol ethers (e.g. ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, dioxane), Examples include aromatic hydrocarbons (eg, benzene, toluene, xylene), aliphatic hydrocarbons (eg, hexane, heptane), nitropropane, and the like.

The base on which this magnetic paint is applied is non-magnetic and can be made of polyester (e.g. polyethylene terephthalate), polyolefin (e.g. polypropylene), cellulose derivatives (e.g. cellulose triacetate, cellulose diacetate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyester. It may be made of hydrazides, metals (eg aluminum, copper), paper, etc.

The thickness of the coating film of the magnetic layer is 0.5 to 6μ after drying.
It is desirable that it is m. This is because if the coating thickness is too thin, it will be difficult to form a uniform coating film, resulting in signal loss, so-called dropouts, and if the coating thickness is too thick, thickness loss will occur due to self-demagnetization. become.

EXAMPLES Below, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

〔Example〕

Cr201 particles 2 parts by weight Carbon black 2 parts by weight Stearic acid 1 part by weight Butyl stearate 1 part by weight Toluene 150 parts by weight Methyl ethyl ketone 150
Part by weight cyclohexanone 60
After kneading and dispersing the above composition in a ball mill for 48 hours, a curing agent (type and amount shown in Table 1) was added,
It was made into a magnetic paint by high-speed shear dispersion.

After applying this magnetic paint for 30 minutes, the thickness was 14 μm and the surface roughness was 0.
．． It was coated on one side of 03 μm polyester terephthalate to a dry thickness of 4.0 μm, and then 2,500 μm
Orientation treatment is performed in a Gauss direct current magnetic field, and the orientation is 80°.
After drying with C, it was subjected to supercalender treatment and further cut into 1/2 inch width to produce a magnetic tape. This magnetic tape was evaluated for its Y-C/N, powder drop, and still time.

The results are shown in Table 2.

In addition, evaluation of Y-C/N, powder falling, and still time was implemented as follows.

CY-C/N) 5MIIz RF ratio output 4 when recording and playing back a 5 MHz RF multiplied signal using a video tape recorder
Ml (the noise ratio near z was set as Y-C/N.

[Powder falling]

After running 100 passes on a VTR, powder falling onto the pinch roller was visually evaluated. The smaller the number, the less powder falls off.

[Still time]

Play in still mode, record the playback RF output level,
The time required for the signal level to drop to 1/2 was measured.

Comparative magnetic tapes were prepared in the same manner as Examples 1 to 7, except that aromatic curing agents as shown in Table 1 were used in place of the curing agents in Examples 1 to 7. was created and evaluated in the same way.

The results are shown in Table 2.

(Continued in the margin on the next page) 1. Types of stone - and he No. λJL'd
Effects of the Invention As detailed above, the durability of the magnetic recording medium of the present invention is significantly improved by sufficient three-dimensional crosslinking.
For example, it is extremely useful for use as a magnetic tape, etc., and has great industrial value.

Claims (1)

[Claims] In a magnetic recording medium having a magnetic layer mainly composed of ferromagnetic powder and a binder on a non-magnetic support, the ferromagnetic powder has a specific surface area of 45 m^2/g or more, and the binder is an aliphatic A magnetic recording medium characterized in that it is cured with a curing agent and/or an alicyclic curing agent.