JP2754703B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a hanging type magnetic recording medium having excellent durability, magnetic powder dispersibility, and recording / reproducing characteristics.

[Related Art] A coating type magnetic recording medium is manufactured by applying a magnetic powder together with a binder resin onto a non-magnetic support to form a magnetic layer. In a coating type magnetic recording medium, it is important to uniformly disperse magnetic powder in a binder resin in order to achieve good recording / reproducing characteristics, and to obtain good durability, a coating of a magnetic layer is required. It is necessary to improve physical properties.

Various surfactants have been studied to improve the dispersibility of the magnetic powder. However, when a surfactant is added, the dispersibility of the magnetic powder is improved, but when added in a large amount, the physical properties of the coating film of the magnetic layer are deteriorated and the durability is adversely affected. Undesirable development such as bleeding out may be caused. On the other hand, if the amount is small, the purpose of improving the dispersibility cannot be achieved in many cases.

[Problems to be solved by the invention]

The present inventors have conducted intensive studies to solve the above problems, and as a result, before mixing the magnetic powder with the binder resin and dispersing it in the binder resin, by pre-kneading with a specific polyester, the durability was improved. The present inventors have found that a magnetic recording medium having excellent magnetic powder dispersibility and recording / reproducing characteristics can be obtained.

[Means for solving the problem]

That is, the gist of the present invention is to provide a magnetic recording medium in which a magnetic layer is formed by applying a magnetic powder together with a binder resin on a non-magnetic support, wherein the magnetic powder comprises at least one of a hydroxyl group, an amino group and a carboxyl group. A magnetic recording medium having at least one functional group, and kneading with a polyester obtained by polymerizing a lactone using a compound having a sulfonic acid metal base as an initiator, and then mixing with a binder resin. Exist.

 Hereinafter, the present invention will be described in detail.

In the present invention, the polyester preliminarily kneaded with the magnetic powder has at least one functional group among a hydroxyl group, an amino group and a carboxyl group, and has a metal sulfonate base (hereinafter, abbreviated as a metal sulfonate-containing compound). .
Is a polyester obtained by subjecting a lactone to ring-opening polymerization using a compound having the following formula:

As the sulfonic acid metal base-containing compound to be used as the initiator, those having a hydroxyl group include 2-hydroxyethanesulfonic acid metal salt, 3-hydroxy-propanesulfonic acid metal salt, 2-hydroxycyclopentanesulfonic acid metal salt, 2-hydroxy Cyclohexanesulfonic acid metal salt, hydroxyethoxybenzenesulfonic acid metal salt, hydroxyethoxybenzenedisulfonic acid bimetallic salt, hydroxyethoxybenzenetrisulfonic acid trimetallic salt, hydroxyethoxytoluenesulfonic acid metal salt, di (hydroxyethoxy) benzenesulfonic acid metal salt Salts, di (hydroxyethoxy) benzenedisulfonic acid bimetallic salt, 5-sulfoisophthalic acid di (2-hydroxyethyl) metal salt,
Di (2-hydroxyethyl) metal salt of 2-sulfoterephthalic acid, bimetallic salt of 4,4'-isopropylidenedi (2-hydroxyethoxy) -X, Y-disulfobenzene, etc .; Metal salt of aminoethanesulfonic acid, metal salt of anilinesulfonic acid, metal salt of anilinedisulfonic acid, metal salt of toluidinesulfonic acid, metal salt of toluidinedisulfonic acid, metal salt of phenylenediaminesulfonic acid, metal salt of phenylenediaminedisulfonic acid, etc .; carboxyl Metal sulfoacetate, dimetal disulfobenzoate, metal sulfophthalate, metal disulfophthalate, metal sulfoterephthalate, metal sulfoisophthalate, etc. having a functional group; Aminophenolsulfonic acid metal salts,
And carboxyphenolsulfonic acid metal salts. As the kind of the metal salt, an alkali metal is preferable, and a sodium salt and a potassium salt are particularly preferable.

Examples of the lactone to be subjected to ring-opening polymerization include β-propiolactone, β-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, β-ethyl-δ-valerolactone, α, β, γ-trimethoxy-δ. Valerolactone, ε-caprolactone, β-methyl-ε-isopropyl-ε-caprolactone and the like. Most preferred lactone monomers are ε-caprolactone and β-methyl-δ-valerolactone.

The ring-opening polymerization of lactone is performed according to a known method depending on the type of lactone and initiator. By this polymerization reaction, a compound in which a sulfonic acid metal base-containing compound has been introduced at one position in the polyester chain can be obtained.

The number average molecular weight of the polyester is preferably from 200 to 50,000. When the molecular weight is larger than 50,000, the dispersibility of the magnetic powder is often disadvantageous. When the molecular weight is smaller than 200, the dispersibility is not problematic but is often disadvantageous in terms of durability.

The pre-kneading can be performed by adding a magnetic powder and the polyester, and if necessary, adding an organic solvent such as methyl ethyl ketone, isobutyl ketone, cyclohexanone, and toluene, and kneading the mixture using a commonly used mixer. it can.

The amount of the polyester is preferably 0.5 to 10 parts by weight based on 100 parts by weight of the magnetic powder. If the addition amount is less than 0.5 parts by weight, the effect on dispersibility improvement is not sufficient,
When the amount is more than the weight part, the content of the magnetic powder is reduced, which adversely affects the electromagnetic conversion characteristics.

Specific examples of the mixer include a device capable of uniformly mixing the magnetic powder and the polyester, such as a stirring blade, a homomixer, a sand mill, a ball mill, a three-roll mill, and a kneader.

By kneading the magnetic powder with the polyester,
The magnetic powder surface is coated with polyester. This polyester has a strong polar sulfonic acid metal base introduced into the molecular chain, so it is strongly adsorbed on the surface of the magnetic powder, and effectively mixes the surface of the magnetic powder even in the subsequent mixing and dispersing process with the binder resin. Can be coated.

As described above, the magnetic powder coated with the polyester is well compatible with the binder resin and the organic solvent used for forming the magnetic layer, and thus has a very good effect on improving the dispersibility of the magnetic powder.

In the magnetic layer, the polyester plays a role as a binder resin, so that the physical properties of the magnetic layer can be improved. Further, polyethylene terephthalate, which is often used as a nonmagnetic support in floppy disks and magnetic tapes, is used. When using a polyester film such as, the familiarity with the base film is good, it is possible to improve the adhesive strength between the magnetic layer and the base film,
The durability of the medium is improved.

As a method for obtaining a polyester into which a sulfonic acid metal base is introduced, there is a method of copolymerizing a diol such as ethylene glycol or propylene glycol with a dicarboxylic acid containing a sulfonic acid metal base. It is difficult to introduce a sulfonic acid metal base-containing compound only at two places, and a plurality of sulfonic acid metal base-containing compounds are introduced at random positions. When the polyester thus obtained is used for pre-kneading with magnetic powder, the crosslinking effect is such that the metal sulfonate base is adsorbed on the surface of the magnetic powder and one molecule of polyester is adsorbed across two or more magnetic powders. , Magnetic powder, a paint-like magnetic composition in which a binder resin and the like are mixed and dispersed in an organic solvent (hereinafter, referred to as a
Abbreviated as magnetic paint. ) Significantly increases the thixotropy and adversely affects the coating process.

In the polyester used in the present invention, since the compound containing a metal sulfonate group is introduced at only one position in one molecule, there is no cross-linking effect between the magnetic powders described above, and the thixotropic property of the magnetic paint does not increase.

As the binder resin used in the present invention, those commonly used for magnetic recording media can be used. Specifically, for example, phenolic resin, epoxy resin, polyurethane curable resin, urea resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin, acrylic resin, polyamide resin, epoxy-polyamide resin, saturated polyester resin, Mixture of high molecular weight polyester resin such as urea formaldehyde resin and other isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, low molecular weight glycol / high molecular weight diol /
Mixtures of the above polycondensation resins with crosslinking agents such as isocyanate compounds, such as mixtures of triphenylmethane triisocyanate; vinyl chloride-vinyl acetate (including those containing polar groups such as carboxyl groups) copolymer resins, vinyl chloride -Vinyl alcohol-vinyl acetate (including those containing polar groups such as carboxyl groups) copolymer resins, vinyl chloride-vinylidene chloride copolymer resins, vinyl chloride-acrylonitrile copolymer resins, vinyl copolymers such as vinyl butyral and vinyl formal A mixture of a cellulose resin and a crosslinking agent; a mixture of a cellulose resin such as nitrocellulose and cellulose acetobutyrate and a crosslinking agent; a mixture of a synthetic rubber resin such as a butadiene-acrylonitrile copolymer resin and a crosslinking agent; These mixtures are mentioned.

As the magnetic powder used in the present invention, magnetic powder conventionally used for magnetic recording media can be used. For example, γ-iron oxide, γ-iron oxide containing cobalt,
Chromium (IV) oxide, metal magnetic powder, barium ferrite and the like can be mentioned.

In the present invention, in addition to the binder resin, polyester, and magnetic powder described above, abrasives such as aluminum oxide and chromium oxide powder, lubricants such as various fatty acids and fatty acids, and conductive materials such as conductive carbon black are used for the magnetic layer. An imparting agent or the like can be contained as needed.

The abrasive is preferably contained in an amount of 1 to 25 parts by weight based on 100 parts by weight of the magnetic powder. If the amount is less than this, the effect as an abrasive is not sufficiently exerted. If the amount is more than this, the surface properties of the magnetic layer are deteriorated, or the content of the magnetic powder is relatively reduced, so that the recording / reproducing characteristics are adversely affected. There is.

The lubricant is preferably contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the magnetic powder. If the amount is less than this, the effect as a lubricant is not sufficiently exhibited, and if it is more than this, bleeding out of the lubricant may occur.

It is preferable that the conductivity imparting agent is contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the magnetic powder. If the amount is less than this, the surface electric resistance of the magnetic recording medium increases, and if it is more than this, the physical properties of the coating film may deteriorate or the durability may deteriorate.

The magnetic recording medium of the present invention includes, for example, magnetic powder preliminarily kneaded with the polyester, a binder resin and, if necessary, an abrasive, a lubricant, a conductivity-imparting agent, and the like, such as methyl ethyl ketone, isobutyl ketone, cyclohexanone, and toluene. After mixing and dispersing with an organic solvent using a mixing and dispersing machine such as a ball mill, a sand mill, and a two-roll to obtain a paint-like magnetic composition, the paint-like composition is placed on a non-magnetic substrate such as polyethylene terephthalate film. , Dried and heat-cured to form a magnetic layer.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist.

Example 1 In a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel and a nitrogen inlet tube, 30 g of 2,5-di (2-hydroxyethoxy) benzenesulfonic acid sodium salt and 1 g of metallic sodium were put and dissolved. Next, 400 g of β-methyl-δ-valerolactone was added and reacted at room temperature for 1 hour to produce a polyester A (number average molecular weight 4000).

Cobalt-containing γ-iron oxide powder 100 parts by weight Polyester A 5 parts by weight Methyl ethyl ketone 65 parts by weight Toluene 65 parts by weight Cyclohexanone 65 parts by weight Stir and mix the above composition for 1 hour using a stirring blade to adsorb polyester A to the magnetic powder. Was.

In addition, polyurethane resin (Nippon Polyurethane “Nipporan”
2304 ") 20 parts by weight Vinyl chloride-vinyl acetate copolymer resin (" VAGH "manufactured by Union Carbide) 20 parts by weight Aluminum oxide powder 10 parts by weight Lubricant 5 parts by weight Conductive carbon black 10 parts by weight Methyl ethyl ketone 45 parts by weight Toluene 45 45 parts by weight of cyclohexanone was added and mixed and dispersed by a sand mill to prepare a magnetic coating material.
A part by weight was added and applied on a 75 μm-thick polyethylene terephthalate film, dried, and then subjected to a surface smoothing treatment. After heat-curing the coating film, it was punched into a disk having a diameter of 3.5 inches to produce a magnetic recording medium.

Example 2 p-phenylenediamine was placed in a four-necked flask equipped with a thermometer, a stirrer, a condenser with a drying tube, and a nitrogen inlet tube.
2,6-disulfonic acid potassium salt 10 g, ε-caprolactone
Add 300 g and 0.1 g of tetraisopropyl titanate, keep the internal temperature at 180 ° C., and react for 18 hours to obtain polyester B
(Number average molecular weight 10,000).

A magnetic recording medium was manufactured in the same manner as in Example 1 except that polyester B was used for the preliminary kneading of the magnetic powder.

Example 3 5 g of 3-carboxybenzenesulfonic acid sodium salt and 400 g of ε-caprolactone were placed in a four-necked flask equipped with a thermometer, a stirrer, a condenser with a drying tube and a nitrogen inlet tube, and the internal temperature was kept at 250 ° C. The mixture was reacted for 24 hours to produce a polyester C (number average molecular weight 19,000).

A magnetic recording medium was manufactured in the same manner as in Example 1 except that polyester C was used for preliminary kneading of the magnetic powder.

Comparative Example 1 Instead of polyester A, soybean lecithin conventionally used as a surfactant (“Honen Lecithin manufactured by Honen Oil Co., Ltd.)
F ") A magnetic recording medium was manufactured in the same manner as in Example 1 except that 5 parts by weight was used.

Comparative Example 2 Cobalt-containing γ-iron oxide powder 100 parts by weight Polyurethane resin (Nipporan Nipporan
2304 ") 20 parts by weight Vinyl chloride-vinyl acetate copolymer resin (" VAGH "manufactured by Union Carbide) 20 parts by weight Polyester A 5 parts by weight Aluminum oxide powder 10 parts by weight Lubricant 5 parts by weight Conductive carbon black 10 parts by weight Methyl ethyl ketone 110 parts by weight Toluene 110 parts by weight Cyclohexanone 110 parts by weight A magnetic recording medium was produced in the same manner as in Example 1 except that the above composition was mixed and dispersed at once using a sand mill to prepare a magnetic coating material.

Comparative Example 3 A three-necked flask equipped with a thermometer, a stirrer and a Claisen tube was charged with 300 g of dimethyl terephthalate, 39 g of dimethyl sodium 5-sulfoisophthalate, 102 g of 1,6-hexanediol, 53 g of ethylene glycol, and calcium acetate.
0.3 g and 0.1 g of antimony trioxide were added, and methanol was distilled off in about 3 hours while maintaining the internal temperature at 180 ° C. In addition, internal temperature 25
After raising the temperature to 0 ° C. and reacting for 1 hour, gradually reducing the pressure to 10 mmHg and reacting for 2 hours, polyester D (number average molecular weight)
9400).

A magnetic recording medium was manufactured in the same manner as in Example 1 except that polyester D was used for the preliminary kneading of the magnetic powder.

The recording / reproducing characteristics (output) and durability of the magnetic recording media manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated, and the results are shown in Table 1.

For the evaluation of the recording / reproducing characteristics (output), the output when a 250 KHz signal was written was measured.
Judgment was made based on the relative value when

The durability was evaluated by continuously rotating the magnetic recording medium obtained under the conditions of a head load of 100 g and a rotation speed of 300 rpm at the outermost track position at room temperature, and observing the generation of scratches on the surface of the magnetic recording medium by the head It was done by doing.
In Table 1, ○ indicates that no scratch was generated even after rotating for 3 hours or more, △ indicates that scratch was generated within 1 to 3 hours of rotation, and x indicates that scratch was generated within 1 hour of rotation. Is shown.

The viscosity of the magnetic paint before being applied to the polyethylene terephthalate film was measured with an E-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), and the thixotropic properties of the paint were evaluated. The results are shown in Table 1. Evaluation of thixotropy is shear rate 19.1se
It was determined by taking the ratio of the viscosity at c ^-1 and 382.8 sec ^-1 (viscosity at 19.1 sec ^{-1 /} viscosity at 382.8 sec ^-1 ).
When this ratio is large, that is, when the rate of change in viscosity due to the change in shear rate is large, the thixotropy is large and the stability of the coating process is poor.

[Effects of the Invention] According to the present invention, a coating type magnetic recording medium having excellent dispersibility and recording / reproducing characteristics of magnetic powder and excellent durability can be obtained, which is industrially useful.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 5/62-5 / 72,5 / 842 C09D 5 / 23,167 / 04

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer formed by applying a magnetic powder together with a binder resin on a non-magnetic support, wherein the magnetic powder comprises at least one of a hydroxyl group, an amino group and a carboxyl group. A magnetic recording medium characterized in that it is kneaded with a polyester obtained by polymerizing lactone using a compound having the above functional group and a metal salt of sulfonic acid as an initiator, and then mixing with a binder resin.