JPH0680526B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk. More specifically, it relates to a magnetic recording medium using a polyester resin and / or a polyurethane resin having excellent properties as a binder component of a magnetic layer provided on a non-magnetic support.

(Prior Art) A magnetic tape, which is a general-purpose magnetic recording medium, has acicular magnetic particles with a long axis of 1 μm or less dispersed in a binder solution together with an appropriate additive (dispersant, lubricant, antistatic agent, etc.). Then, a magnetic paint is made, and this is applied to polyethylene terephthalate film.

The properties required for the binder of the magnetic recording medium are the dispersibility / fillability / orientation of the magnetic particles, durability / wear resistance / heat resistance / smoothness of the magnetic layer, and adhesion to the non-magnetic support. The binder plays a very important role. Conventionally used binders for magnetic particles include vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate /
Vinyl alcohol copolymer, vinyl chloride / vinylidene chloride copolymer, polyurethane resin, polyester resin, acrylonitrile / butanediene copolymer, nitrocellulose, cellulose acetate / butyrate, epoxy resin, acrylic resin, etc. are used. Among these resins, polyurethane resin is superior in toughness compared to other resins due to intermolecular hydrogen bond by urethane bond, but conventional adipate type or caprolactone type polyurethane resin alone has blocking resistance and heat resistance. , Inferior characteristics such as running stability. Therefore, a mixed system of a polyurethane resin and nitrocellulose or a vinyl chloride / vinyl acetate copolymer is used.
However, the durability, abrasion resistance, heat resistance, and other characteristics are still insufficient in fields requiring high performance such as video tapes, computer tapes, and floppy disks.
It is known to increase the urethane group concentration in order to improve these characteristics, but in this case, it becomes insoluble in the above-mentioned general-purpose organic solvent, and high boiling point solvents such as dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide, Soluble only in cyclic ethers such as tetrahydrofuran and dioxane. These high-boiling point, high-polarity solvents cause serious problems such as swelling / curving or dissolution of the non-magnetic support, and poor dryability, which lowers workability.

In order to eliminate the drawbacks found in conventional adipate-type or caprolactone-type thermoplastic polyurethane resins, the so-called two-component method is known, in which a hydroxyl group terminated polyurethane resin undergoes a curing reaction with a polyisocyanate compound and an isocyanate terminated polyurethane resin undergoes a curing reaction with a polyol compound. Has been. However, when these terminal groups are used as the crosslinking points, sufficient improvement in heat resistance and solvent resistance cannot be seen because the crosslinking density is low. Further, there is a drawback that a high temperature is required for crosslinking by an allophanate formation reaction which is a reaction between a urethane group and an isocyanate group. Even in the conventional magnetic recording medium, a method of curing the hydroxyl group-terminated thermoplastic polyurethane resin used as the binder with a polyisocyanate compound is used in order to improve the properties such as heat resistance and durability of the magnetic layer. The current situation is that I cannot say.

Various improvements have been made to the thermoplastic polyurethane resin in order to improve the crosslink density of the cured product obtained by the two-component method. For example, glycerin is a part of the raw material of polyurethane resin,
It is known to use a trifunctional or higher functional polyol such as trimethylolpropane or pentaerythritol to prepare a branched polyurethane resin. However, the properties of the cured product of this branched polyurethane resin improve depending on the amount of the trifunctional or higher functional polyol component used, but in this case, there is a greater tendency to gel during the production of the branched polyurethane resin.

Further, a thermoplastic polyurethane resin which has been conventionally used has a great drawback as a binder for a magnetic layer that, when used as a binder for a magnetic layer, the dispersibility of magnetic particles is poor.

When a polyester resin is used as a binder for the magnetic layer, it has excellent adhesiveness with a polyethylene terephthalate film, which is a general-purpose non-magnetic support, but has poor wear resistance, running durability, and other characteristics, and it is also versatile. Similar to the thermoplastic polyurethane resin, it has a drawback that the dispersibility of magnetic particles is poor.

(Problems to be Solved by the Invention) In the magnetic recording medium, in order to maximize the characteristics of the magnetic particles, it is necessary that the magnetic particles are dispersed to the level of each magnetic particle. In recent years, there has been a tendency to use metal particles as magnetic particles and to make magnetic particles finer in order to increase recording density and improve S / N ratio. Dispersion is poor and sufficient characteristics as a magnetic recording medium cannot be obtained.

In addition, the smoothness of the magnetic layer is required to increase the recording density and the S / N ratio, but as the smoothness is improved, the characteristics such as durability, wear resistance, and running stability are improved. More importantly, the conventional magnetic recording medium has a problem that these characteristics are still insufficient.

(Means for Solving Problems) To achieve the object of the present invention, which is to provide a magnetic recording medium having excellent dispersibility of magnetic particles and excellent durability, wear resistance, and running stability of a magnetic layer. As a result of diligent studies on polyester resins and polyurethane resins, it was found that this can be achieved by including a polyester resin and / or a polyurethane resin having a phenolic hydroxyl group in the molecule as a binder component of magnetic particles.

That is, the present invention relates to a magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is coated on a non-magnetic support, and a polyester resin having a phenolic hydroxyl group in the molecule as a component of the binder and / or A magnetic recording medium comprising a polyurethane resin.

Further, a part of the phenolic hydroxyl group in the polyester resin or polyurethane resin may be ionized.

As the dicarboxylic acid component and the diol component used in the production of the polyester resin used in the present invention, those containing a phenolic hydroxyl group as an essential component are used.

Examples of the dicarboxylic acid component and diol component containing a phenolic hydroxyl group include compounds represented by the following general formulas (I) to (VIII) or derivatives thereof.

Examples of such compounds include the following.

3-hydroxyorthophthalic acid, 4-hydroxyorthophthalic acid, 3,4-dihydroxyorthophthalic acid, 3,5-dihydroxyorthophthalic acid, 4-hydroxyisophthalic acid, 5-hydroxyisophthalic acid, 4,5-dihydroxyisophthalic acid Acid, 2-hydroxyisophthalic acid, 2-hydroxyterephthalic acid, 2,3-dihydroxyterephthalic acid, 2,5-dihydroxyterephthalic acid, 2,3-bishydroxyethylphenol, 2,4-bishydroxyethylphenol, 2, 5-bishydroxyethylphenol, 2,6
-Bishydroxyethylphenol, 2,3-bis (hydroxyethoxy) phenol, 2,4-bis (hydroxyethoxy) phenol, 2,5-bis (hydroxyethoxy) phenol, 2,6-bis (hydroxyethoxy) phenol, 4-hydroxyorthophthalic acid bishydroxyethyl ester, p-oxybenzoic acid-1,3-dihydroxyisopropyl ester, p-oxybenzoic acid-2,
Examples include 3-dihydroxypropyl ester and p-hydroxybenzoic acid ester of 1,1,1-tri (hydroxymethyl) propane.

Other carboxylic acid components of the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-naphthalenedicarboxylic acid, and aliphatic carboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid. Dicarboxylic acid etc. can be mentioned.

As the glycol component, 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, cyclohexanedimethanol, ethylene oxide adduct and propylene oxide adduct of bisphenol A, ethylene oxide adduct and propylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene For example, glycol.

As raw material components for polyester resins other than the above, dicarboxylic acids containing a sulfonic acid metal base such as 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid and sodium sulfoterephthalic acid, and the following general formulas [I] and [II] ] The phosphorus-containing compound shown by these is mentioned.

(In the formula, R ₁ is a monovalent ester-forming functional group. R ₂ ,
R ₃ is the same or different and has 1 to 10 carbon atoms.
Selected from the group consisting of a monovalent hydrocarbon group, a halogen atom and a monovalent ester-forming functional group. A represents a divalent or trivalent organic residue. N ₁ represents 1 or 2, and n ₂ and n ₃ each represent an integer of 0-4. ) (In the formula, R ₄ is a hydrogen atom, a carbon-hydrogen group having 1 to 12 carbon atoms which may contain an ester-forming functional group, or M ₂ O. R ₅ is a divalent or trivalent group having 1 to 6 carbon atoms. Hydrocarbon group, R ₆ is a hydrogen atom, a hydrocarbon group having 1 to 12 carbon atoms which may contain a hydrogen group or M _3, M ₁ , M ₂ and M ₃ are alkali metal atoms, and m is 0 or 1, l. Represents an integer of 1 or 2.) Metal sulfonate group-containing compounds, general formulas [I] and [II]
When the phosphorus-containing compound represented by is used as at least one component of the raw material, it is effective in greatly improving the drawbacks of the conventional inorganic resin and the low dispersibility of the filler, which are found in the polyester resin. When it is used as a binder of a magnetic layer in a magnetic recording medium, the dispersibility of the magnetic particles is improved, and the characteristics resulting from the dispersibility of the magnetic particles, such as the electromagnetic conversion characteristics of the magnetic recording medium, are greatly improved.

The polyurethane resin used in the present invention is obtained by the reaction of a diol component and an organic diisocyanate, and contains a phenolic hydroxyl group in the molecule. As a method of introducing a phenolic hydroxyl group, a method of using the above-mentioned phenolic hydroxyl group-containing polyester resin as one component of a raw material or a phenolic hydroxyl group-containing diol, for example, represented by the general formulas (II), (IV) to (VIII) The method of using a compound is mentioned.

As the polyurethane resin used in the present invention, raw material components containing no phenolic hydroxyl group may be used in addition to the above raw materials. Examples of the long chain diol component include polyester diol, polyether diol, polycarbonate diol and the like, and chain extenders include glycols, amino alcohols, diamines and hydrogen.

Examples of the organic diisocyanate used in the production of the polyurethane resin used in the present invention 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'-biphenylene diisocyanate, 2,4-naphthalene diisocyanate,
3,3'-Dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate Examples thereof include isocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-diisocyanate methylcyclohexane, 4,4-diisocyanate dicyclohexane, 4,4-diisocyanate cyclohexylmethane and isophorone diisocyanate.

The content of the phenolic hydroxyl group in the polyester resin or polyurethane resin used in the present invention is 20 equivalents in the resin.
/ 10 ⁶ g or more, particularly 100 equivalent / 10 ⁶ g is preferable. If the amount of the phenolic hydroxyl group is less than 20 equivalent / 10 ⁶ g, the effect of containing the phenolic hydroxyl group is not observed.

The phenolic hydroxyl group in the polyester resin or polyurethane resin used in the present invention may partially become an anion due to a strong base such as sodium hydroxide or potassium hydroxide. By being anionized, the dispersibility of the magnetic particles is improved, but when the two-liquid method is used, abrasion resistance and heat resistance are reduced. The anionization rate is preferably 50% or less of all phenolic hydroxyl groups.

In the present invention, the polyester resin used in the present invention,
In addition to the polyurethane resin, for the purpose of adjusting flexibility, improving cold resistance, heat resistance, etc., other resin is added and / or a compound which reacts with the thermoplastic polyurethane resin and crosslinks is mixed. Is desirable. Examples of other resins include vinyl chloride resins, polyester resins, cellulose resins, epoxy resins, phenoxy resins, polyvinyl butyral, acrylonitrile / butadiene copolymers, and the like. On the other hand, as the polyester resin and the compound that crosslinks with the polyurethane resin, there are polyisocyanate compounds, epoxy resins, melamine resins, urea resins, and the like,
Of these, polyisocyanate compounds are particularly desirable.

The ferromagnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe ₂ O ₃ , mixed crystals of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , and Cr.
Examples thereof include O ₂ , cobalt-doped γ-Fe ₂ O ₃ or Fe ₃ O ₄ , barium ferrite, and ferromagnetic alloy powders such as Fe—Co and Fe—Co—Ni.

In the coating layer of the magnetic recording medium of the present invention, if necessary, a plasticizer such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfosodium succinate, t-butylphenol polyethylene ether, ethylnaphthalene sodium sulfonate, dilauryl succinate. It is also possible to add lubricants such as nate, zinc stearate, soybean oil lecithin, silicone oil and various antistatic agents.

(Function) The polyester resin and / or polyurethane resin used as at least one component of the binder of the magnetic layer in the present invention has a phenolic hydroxyl group in the molecule. The polyester resin and polyurethane resin used in the present invention are excellent in the adsorptivity to the magnetic particles due to the phenolic hydroxyl group, and as a result, the magnetic recording medium of the present invention has good dispersibility of the magnetic particles.

Since the reaction rate of the phenolic hydroxyl group and the isocyanate group is slower than that of the alcoholic hydroxyl group and the isocyanate group, there is less risk of gelation during the production of polyurethane. Further, when polyisocyanate is used as a curing agent, there is an advantage that the pot life becomes long, while
A cross-linking reaction is caused by a curing treatment after drying with a solvent, and as a result, the magnetic recording medium of the present invention has improved properties such as durability, abrasion resistance and heat resistance.

The polyester resin and / or polyurethane resin having a phenolic hydroxyl group of the present invention is easier to produce than a resin having an alcoholic hydroxyl group, and more hydroxyl groups can be introduced into the molecule. As a result, the dispersibility of the magnetic particles is further excellent as a magnetic recording medium.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples. In the examples, "parts" means "parts by weight".

Polyester resin synthesis examples 1-3 and comparative synthesis example 1,
2 175 parts of dimethyl terephthalate, 175 parts of dimethyl isophthalate, 36 parts of 5-hydroxyisophthalic acid, 149 parts of ethylene glycol, 166 parts of neopentyl glycol and 0.14 parts of tetrabutoxytitanium are charged into 2 autoclaves and esterified at 200 to 230 ° C for 4 hours. A chemical reaction and a transesterification reaction were carried out. Then, raise the temperature to 250 ° C over 30 minutes and gradually reduce the pressure, distill off excess glycol at 250 ° C and 10 mmHg, and finally perform polycondensation reaction at 260 ° C and 0.1 to 0.3 mmHg for 90 minutes to obtain a brown polyester resin. Got
As a result of measurement by gel permeation chromatography, the molecular weight was 16,000 in terms of polystyrene. Resin composition is NMR
The results are shown in Table 1.

Similarly, using the raw materials shown in Table 1, polyester resins 2 to 3 containing phenolic hydroxyl groups and polyester resins 1 and 2 containing no phenolic hydroxyl groups were obtained. The composition is as shown in Table 1.

Polyurethane Resin Synthesis Examples 1 to 7, Comparative Synthesis Examples 1 to 4 In a reaction vessel equipped with a thermometer, a stirrer, and a reflux type cooling tube,
Polyester Resin Synthesis Example 1 100 parts of the phenolic hydroxyl group-containing polyester resin (however, molecular weight 2,000) was thoroughly dried and then charged, and further 100 parts of polybutylene adipate having a molecular weight of 2,000 and neopentyl glycol 15
Parts, toluene 100 parts, methyl ethyl ketone 100 parts,
After dissolution, 4,4'-diphenylmethane diisocyanate 60
Parts, 0.04 parts of dibutyltin dilaurate as a reaction catalyst were added, and after reacting at 75 ° C. for 6 hours, 221 parts of toluene and 221 parts of methyl ethyl ketone were added to obtain a brown polyurethane solution having a solid content concentration of 30%. The molecular weight of the polyurethane resin was 27,000 in terms of polystyrene.

Similarly, a phenolic hydroxyl group polyurethane resin was obtained using the raw materials shown in Table 2. Further, using the raw materials shown in Table 2, polyurethane resins containing no phenolic hydroxyl groups were obtained by Comparative Synthesis Examples 1 to 4.

Polyurethane Resin Synthesis Example 8 100 parts of the phenolic hydroxyl group-containing polyester resin (however, molecular weight 2,000) obtained in Synthesis Example 1 of polyester resin and toluene in the same reaction vessel as in Synthesis Example 1 of polyurethane resin
After charging 150 parts and dissolving, 1N-sodium hydroxide aqueous solution 1
After adding 5 g, heat and azeotropically evaporate toluene / water to 55
It was excluded from the g system. Furthermore, 100 parts of polybutylene adipate having a molecular weight of 2,000, 15 parts of neopentyl glycol, 100 parts of methyl ethyl ketone and 0.005 g of phosphorous acid are added, 60 parts of 4,4′-diphenylmethane diisocyanate, and 0.04 parts of dibutyltin dilaurate as a reaction catalyst are added, 75 After reacting for 6 hours at ℃, add 221 parts of triene, 221 parts of methyl ethyl ketone,
A brown polyurethane solution having a solid content of 30% was obtained. The molecular weight of the polyurethane resin was 2,600 in terms of polystyrene.

Example 1 A polyester resin (Synthesis Example 1) was used, and a composition having the following blending ratio was placed in a ball mill and dispersed for 48 hours.
Isocyanate compound Coronate 2030 (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added as a curing agent in an amount of 5 parts and further mixed for 1 hour to obtain a magnetic coating material. This was applied onto a polyethylene terephthalate film having a thickness of 12 μm while applying a magnetic field of 2000 glass so that the thickness after drying would be 5 μm. 60
After being left for 1 day at ℃, it was slit into a 1/2 inch width to obtain a magnetic tape.

Polyester resin (I) solution (solid content 30%, MEK / toluene = 1/1 solution) 100 parts Cobalt-deposited γ-Fe ₂ O ₃ 120 parts Olive oil 1 part MEK 100 parts Cyclohexanone 50 parts Toluene 50 parts Example 2 -17, Comparative Examples 1-10 Instead of the polyester resin (Synthesis Example 1) used in Example 1, polyester resin (Synthesis Examples 2-3), polyurethane resin (Synthesis Examples 1-8) and polyester resin (comparative synthesis) Examples 1-2), polyurethane resin (Comparative Synthesis Example 1-4)
A magnetic tape was obtained in the same manner as in Example 1.

Table 3 shows the characteristics of the magnetic tapes of the above Examples and Comparative Examples.

(Effect of the Invention) A polyester resin or a polyurethane resin containing a phenolic hydroxyl group in the molecule has excellent dispersibility with magnetic particles and good reactivity with a curing agent. The magnetic recording medium of the present invention used as
As is clear from the examples, magnetic recording media excellent in durability, wear resistance, electromagnetic conversion characteristics, S / N ratio, surface smoothness, etc. can be obtained.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a nonmagnetic support coated with a magnetic material in which a ferromagnetic powder is dispersed in a binder,
A magnetic recording medium comprising a polyester resin and / or a polyurethane resin having a phenolic hydroxyl group in the molecule as a component of the binder. 2. The magnetic recording medium according to claim 1, wherein a part of the phenolic hydroxyl group in the polyester resin and / or the polyurethane resin is ionized.