JP2701303B2 - Magnetic recording media - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having significantly improved durability.

[Summary of the Invention]

The magnetic recording medium of the present invention has a significantly improved durability by using a ferromagnetic powder having a specific specific surface area and using a specific binder and a specific curing agent.

[Conventional technology]

Conventionally, an aromatic isocyanate (TDI) -based curing agent such as Coronate L (trade name, manufactured by Nippon Polyurethane Co., Ltd., TDI-based curing agent) that reacts with a hydroxyl group in a binder is used to improve the durability of a magnetic recording medium. I have been. Since Coronate L is a trifunctional isocyanate compound, it reacts with a side chain or a terminal hydroxyl group of the binder, and can form a three-dimensional network structure.

[Problems to be solved by the invention]

However, since a TDI-based curing agent such as Coronate L has a very high reactivity, when a specific binder into which a polar group is introduced is used, not only the side chain and the terminal hydroxyl group of the binder, It may react with water in the paint or water adsorbed on the surface of the magnetic powder. If the isocyanate group of the curing agent reacts with water before the hydroxyl group of the binder, the effective isocyanate group that reacts with the hydroxyl group of the binder decreases, and it becomes impossible to make three-dimensional crosslinking. .

Further, the above phenomenon is caused by Co deposition γ having a specific surface area of 45 m ² / g or more.
-Fe ₂ O ₃ and metallic magnetic powder were particularly microscopic.

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

[Means for solving the problem]

The present inventor is a polyester resin having a polar group introduced,
If a binder selected from a polyurethane resin in which a polar group is introduced and a vinyl chloride resin in which a polar group is introduced, and if the specific surface area of the ferromagnetic powder is selected to be 45 to 60 m ² / g, TDI, such as Coronate L, which has been commonly used as all or part of a curing agent in this type of magnetic recording medium
The present inventors have found that the binder can be sufficiently three-dimensionally crosslinked in a state where the ferromagnetic powder is very well dispersed without using a system curing agent, and the present invention has been completed. Therefore,
The present invention provides a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a nonmagnetic support, wherein the ferromagnetic powder has a specific surface area of 45 to 60 m ² / g, and the binder Is a polyester resin in which a polar group is introduced, a polyurethane resin in which a polar group is introduced, and a vinyl chloride resin in which a polar group is introduced, and the binder is a resin group isocyanate compound and And / or cured only with a curing agent comprising an alicyclic isocyanate compound.

In the present invention, as described above, the ferromagnetic powder constituting the magnetic layer has a specific surface area of 45 to 60 m ² / g by the BET method. This means that particles with a specific surface area of less than 45 m ² / g can not expect much of an effect of improving S / N, and particles larger than 60 m ² / g are difficult to disperse well in the binder. That's why. Further, when the modulation noise was measured, it was found that when the specific surface area was 45 m ² / g or more, a desired low noise level was obtained even at a short wavelength of 1 μm or less.

The ferromagnetic powder used in the present invention is Fe, Fe-Co, Fe-Co
-Ni or the like, or a needle-like metal powder containing a small amount of an additional element such as Al, Cr, or Si in consideration of, for example, corrosion resistance or prevention of sintering at the time of production can be used. These acicular metal powder, acicular iron oxide as the starting material, hydrated iron oxide, optionally Ni, iron oxide or hydrated iron oxide in a reducing atmosphere such as H ₂ gas containing a metal such as Co And can be obtained by reduction. The specific surface area of the ferromagnetic powder can be controlled by selecting the specific surface areas of the above-mentioned starting materials.

The binder used in the present invention is selected from a polyester resin having a polar group introduced therein, a polyurethane resin having a polar group introduced therein, and a vinyl chloride resin having a polar group introduced therein. These resins can be obtained by various methods. For example, a sulfonic acid metal base-containing polyester resin can be obtained by using a dicarboxylic acid containing a sulfonic acid metal base as a part of a dicarboxylic acid component, and condensing it with a diol having no sulfonic acid metal base together with a diol. it can. The polyurethane resin containing a metal sulfonate group can be obtained by a condensation reaction and an addition reaction using three kinds of starting materials of the above-mentioned polyester containing a metal sulfonate group together with diisocyanate. Furthermore, a method of modifying a polyester resin, a polyurethane resin, or a vinyl chloride resin to introduce a polar group can be considered. In other words, with these resins, for _{example, Cl-CH 2 CH 2 SO} 3 M, Cl-CH 2 CH 2 OSO 3 M, And the like, and a compound containing the above-mentioned polar group and chlorine is condensed by a dehydrochlorination reaction and introduced.

As the carboxylic acid component used in the present invention to obtain a polyester resin and a polyurethane resin,
Terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-
Aromatic dicarboxylic acids such as naphthalic acid, aromatic oxycarboxylic acids such as p-hydroxybenzoic acid, p- (hydroxyethoxy) benzoic acid, and aliphatic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid Examples thereof include tricarboxylic acids such as dicarboxylic acid, trimellitic acid, trimesic acid, and pyromellitic acid, and tetracarboxylic acids. Particularly, terephthalic acid, isophthalic acid, adipic acid and sebacic acid are preferred.

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

The diol component includes ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2 , 2,4-trimethyl-1,3
-Pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.

As the diisocyanate component used in the present invention to obtain a polyurethane resin, 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'-diphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4 '
-Diisocyanate-diphenyl ether, 1,3-naphthalenediisocyanate, p-xylylenediisocyanate, m-xylylenediisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatedicyclohexane, 4 4,4'-diisocyanate dicyclohexylmethane, isophorone diisocyanate and the like. .

When a vinyl chloride resin is modified to introduce a sulfonic acid metal base, vinyl chloride resin may be used as the vinyl chloride resin.
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-
Vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer and the like are used. And the vinyl alcohol contained in these
And OH _{groups, Cl-CH 2 CH 2 SO} 3 M, sulfonic acid metal salt containing chlorine, such as Cl-SO ₃ M and chlorine, dimethylformamide, pyridine in a polar solvent such as dimethyl sulfoxide, picoline, triethylamine, etc. A method of performing a dehydrochlorination reaction in the presence of a dehydrochlorinating agent such as an amine, an epoxy compound such as ethylene oxide and propylene oxide.

In the present invention, the number average molecular weight of the binder is 50,000
The following is preferred. This is because, when the number average molecular weight exceeds 50,000, when the specific surface area of the magnetic powder by the BET method increases, the viscosity of the coating material becomes too large beyond an allowable range. And the number average molecular weight of the binder is
2,000 or more is preferred. This means that the number average molecular weight is 2,000
If the content is below, when the magnetic coating material is applied on the support and then cured using a curing agent, unreacted components are generated, and low molecular weight components remain to deteriorate the physical properties of the coating film.

In the present invention, the polar group-containing binder preferably has a molecular weight of 200 to 50,000 per polar group. This is because if it is less than 200, the hydrophilicity of the resin is too strong, the solubility in the solvent, the compatibility with the other resin in the binder and the moisture resistance of the magnetic layer deteriorate, and on the other hand, 50,000 This is because the effect on dispersibility becomes insufficient if the above is satisfied.

Further, the weight ratio P / B of the ferromagnetic powder and the binder constituting the magnetic layer is selected from 3 to 12, preferably from 4 to 8. This is because if the amount of the binder is too large, that is, if the P / B is too small, the residual magnetic flux density Br will be insufficient and the S / N will not be improved, and if the P / B is too large, the powder will fall off. Is increased and durability is deteriorated.

The curing agent used in the present invention comprises an aliphatic isocyanate compound and / or an alicyclic isocyanate compound. The curing agent composed of the aliphatic isocyanate compound may be any generally known curing agent, for example, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMDI), coronate EH (products Name, Nippon Polyurethane Co., HDI type) Coronate HL (trade name, Nippon Polyurethane Co., HDI type), Takenate D-170N
Takeda Pharmaceutical Co., HDI system). The curing agent comprising an alicyclic isocyanate compound may be any known one as long as it is generally known, for example, isophorone diisocyanate (IPDI), bis (isocyanatomethyl) cyclohexane (HXDI), takenate D-140N (trade name, manufactured by Takeda Pharmaceutical Co., Ltd., IPDI system). Of these, coronate EH and coronate HL are preferred for the curing agent composed of an aliphatic isocyanate compound, and Takenate D-140N is preferred for the curing agent composed of an alicyclic isocyanate compound. It is used alone or in a mixed system.

The mixing ratio of this curing agent is usually 5 to 50 parts by weight based on 100 parts by weight of the total amount of the binder. If the proportion is less than 5 parts by weight, the crosslinking property is not sufficient, and the durability is poor. If the proportion exceeds 50 parts by weight, the coating properties are deteriorated. Preferably it is 10 to 40 parts by weight.

Further, to the magnetic layer, aluminum oxide, chromium oxide, or silicon oxide can be added as a reinforcing agent, 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 on a non-magnetic base.
In that case, ketones (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone,
Cyclohexanone), alcohols (eg, methanol, ethanol, propanol, butanol), esters (eg, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate, monoethyl ether), glycol ethers (eg, ethylene glycol dimethyl ether, ethylene) Glycol monoethyl ether, dioxane), aromatic hydrocarbons (eg, benzene, toluene, xylene),
Aliphatic hydrocarbons (for example, hexane, heptane), nitropropane and the like can be mentioned.

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

The thickness of the coating film of the magnetic layer after drying is 0.5 to 6 μm.
m is desirable. This is because if the coating thickness is too small, it becomes difficult to form a uniform coating film, and signal loss or so-called dropout occurs.If the coating thickness is too large, thickness loss due to self-demagnetization occurs. become.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

〔Example〕

Examples 1 to 7 100 parts by weight of ferromagnetic powder (types shown in Table 1) (specific surface area: 45 m ² / g axis ratio: 11 to 13) 10 parts by weight of vinyl chloride copolymer (degree of polymerization: 420, vinyl chloride) content: 88 wt%, - OH: 0.085 mmol / g, -SO ₃ Na: 0.04 mmol / g) 10 parts by weight polyester polyurethane resin (-SO ₃ Na: 0.05 mmol / g) Cr ₂ O ₃ 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 parts by weight Cyclohexanone 60 parts by weight After kneading and dispersing the above composition in a ball mill for 48 hours, a curing agent (type shown in Table 1) And the amount) were added, and the mixture was sheared at a high speed to obtain a magnetic paint.

After 30 minutes, the magnetic paint is 14 μm thick and has a surface roughness of 0.03 μm.
Dry thickness of 4.0 μm on one side of polyester terephthalate
μm, and then subjected to an orientation treatment in a DC magnetic field of 2,500 Gauss, dried at 80 ° C., subjected to a super calender treatment, and further cut into a 1/2 inch width to prepare a magnetic tape. About this magnetic tape,
C / N, powder drop, and still time were evaluated.

 The results are shown in Table 2.

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

[Y-C / N]

Using a video tape recorder, a 5 MHz RF signal was recorded and reproduced, and the ratio between the 5 MHz RF output and the noise near 4 MHz was YC / N.

[Powder drop]

The powder falling to the pinch roller after running 100 passes with a VTR was visually evaluated. The smaller the value, the smaller the amount of powder falling.

[Still time]

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

Comparative Examples 1 to 3 Except for using an aromatic curing agent and / or a ferromagnetic powder having a small specific surface area as shown in Table 1 in place of the curing agent and / or the ferromagnetic powder in Examples 1 to 7, Example 1
A magnetic tape for comparison was prepared in the same manner as in No. 7, and evaluated similarly. The results are shown in Table 2.

According to the magnetic recording medium of the present invention, a bond selected from a polyester resin having a magnetic group introduced, a polyurethane resin having a polar group introduced, and a vinyl chloride resin having a polar group introduced therein And the specific surface area of the ferromagnetic powder
Since the binder was selected to be 45 to 60 m ² / g, the magnetic powder was extremely hardened even though the binder was hardened only with a hardener composed of an aliphatic isocyanate compound and / or an alicyclic isocyanate compound. The binder can be sufficiently three-dimensionally cross-linked in a well-dispersed state, so that the durability of the magnetic recording medium can be remarkably improved, and therefore, it is extremely useful, for example, as a magnetic tape. And its industrial value is extremely large.

Claims (1)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder on a nonmagnetic support, wherein the ferromagnetic powder has a specific surface area of 45 to 60 m ² / g. The agent is selected from a polyester resin having a polar group introduced, a polyurethane resin having a polar group introduced, and a vinyl chloride resin having a polar group introduced, and the binder is an aliphatic isocyanate compound. And / or a magnetic recording medium cured with only a curing agent comprising an alicyclic isocyanate compound.