JPH02116021A - magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium which is uniformly dispersed with magnetic powder, has good surface characteristics and exhibits excellent electromagnetic conversion characteristics by incorporating a specific vinyl copolymer and specific polyurethane resin into a magnetic layer. CONSTITUTION:The vinyl copolymer consisting of (a) a vinyl chloride unit, (b) a vinyl monomer unit the side chain of which is a hydroxyl group-contg. monovalent org. group, (c) a vinyl monomer unit the side chain of which is a -SO3M group or a monovalent org. group having the -SO3M group (M is a hydrogen atom or metal atom), and (d) a vinyl copolymer consisting of a vinyl monomer unit having an epoxy group in the side chain is incorporated into the magnetic layer. The polyurethane resin having the metal salt group of sulfonic acid is incorporated therein together with the above-mentioned copolymer. The ratio of the (a) unit is preferably 50 to 95wt.%, the ratio of the (b) unit is 1 to 15wt.%, the ratio of the (c) unit is 0.5 to 10wt.%, and the ratio of the (d) unit is 0.1 to 20wt.%, respectively. The magnetic recording medium which is uniformly dispersed with the fine magnetic powder and has the good surface characteristics and the excellent electromagnetic conversion characteristics is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks that perform high-density magnetic recording.

(Prior art and its problems) Magnetic recording media generally consist of a support and a magnetic layer obtained by coating the support with a magnetic paint containing magnetic powder, a binder, etc. and drying it. In order for the medium to exhibit excellent electric WL conversion characteristics, it is desirable that the magnetic particles be uniformly dispersed in the magnetic layer and that the medium surface be smooth.

Therefore, various binders and dispersants have been proposed to improve the dispersibility of magnetic powder in the production of magnetic tapes using T-iron oxide, etc., and barium ferrite magnetic powder also uses these agents. technology is applied.

However, unlike acicular magnetic powder such as γ-iron oxide, barium ferrite magnetic powder has a hexagonal plate-like particle shape, so conventionally used binders and dispersants have not always been effective.

On the other hand, in recent years, with the demand for higher density magnetic recording, efforts have been made to make barium ferrite magnetic powder ultrafine and improve its specific surface area, and the recording wavelength has become shorter and the track width has been compressed, resulting in rapid miniaturization of media. is progressing to

For this reason, conventional media technology is no longer able to adequately address this issue, and it has become difficult to obtain magnetic recording media with uniformly dispersed magnetic powder particles, good surface properties, and excellent electromagnetic conversion characteristics. .

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems and provide a magnetic recording medium in which magnetic powder particles are uniformly dispersed, the surface properties are good, and the electromagnetic conversion characteristics are excellent.

(Means for Solving the Problems) As a result of studying various binders to improve the dispersibility of barium ferrite magnetic powder, the present inventors found that a specific vinyl copolymer and a specific polyurethane were used in the magnetic layer. It has been found that by containing a resin, a magnetic recording medium can be obtained in which the magnetic powder is uniformly dispersed, the surface properties are good, and the electromagnetic conversion characteristics are excellent.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing barium ferrite magnetic powder is provided on a support, in which the magnetic layer contains: (i) a vinyl copolymer consisting of each of the following structural units; ) a vinyl chloride unit, (b) a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group, (c) a monovalent organic group whose side chain is a -SO3M group or a -SO3M group (M in the formula is a hydrogen atom or a metal atom), (b) a vinyl monomer unit having an epoxy group in the side chain, and (ii) a polyurethane resin having a sulfonic acid metal base. The present invention relates to a magnetic recording medium characterized by:

The vinyl copolymer in the present invention includes the above-mentioned (a) to
It is composed of each unit of (d).

The unit (a) is a vinyl chloride unit which is the main constitutional unit of the vinyl copolymer. (a) The unit ratio is 50-95
Weight percent is preferred. If the amount of the (a) unit is too small, the physical strength of the magnetic layer will decrease, and if it is too large, the solubility of the vinyl copolymer will decrease, which is not preferable.

(b) The unit is a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group.

(b) Monomers corresponding to the unit include hydroxypropyl acrylate, hydroxyethyl methacrylate,
Examples include 2-hydroxypropyl methacrylate and N-methylolacrylamide.

The proportion of the unit (b) is preferably 1 to 15% by weight. (B)
If the amount of units is too small, the dispersibility of the magnetic powder will decrease and the compatibility with the polyurethane resin will also decrease. On the other hand, if the amount is too large, the durability of the magnetic layer decreases, which is not preferable.

(c) The unit is a monovalent organic group whose side chain has a -30,M group or -SO3M group (M in the formula is a hydrogen atom or a metal atom)
It is a vinyl monomer unit.

Examples of the monomer corresponding to the unit (c) include vinylsulfonic acid, arylsulfonic acid, alkylarylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, allyldodecylsulfosuccinate, etc. Examples include alkali metal salts.

(c) The proportion of units is preferably 0.5 to 10%.

Outside this range, the dispersibility of the magnetic powder decreases, which is not preferable.

The unit (d) is a vinyl monomer unit having an epoxy group in its side chain.

(d) Monomers corresponding to the unit include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methacryl glycidyl ether, unsaturated acids such as glycidyl acrylate, glycidyl methacrylate, and glycidyl ethyl maleate. glycidyl esters,
Examples include epoxide olefins such as butadiene monooxide and vinylcyclohexene monooxide.

The proportion of the unit (d) is preferably 0.1 to 20% by weight.

Outside this range, the dispersibility of the magnetic powder decreases, which is not preferable.

The average degree of polymerization of the vinyl copolymer composed of each of the units (a) to (b) described above is preferably 100 to 1000. If the average degree of polymerization is too low, the physical strength of the magnetic layer will decrease, If it is too high, the viscosity of the solution becomes high and workability becomes poor, which is not preferable.

The vinyl copolymer of the present invention can be produced by a general suspension polymerization method, emulsion polymerization method, solution polymerization method, bulk polymerization method, or the like.

The vinyl copolymer in the present invention includes the above-mentioned (a) to
In addition to the structural unit (d), various structural units may be contained in order to improve the solubility and flexibility of the copolymer. For example, vinyl esters such as vinyl acetate and vinyl propionate, ethyl vinyl ether, isobutyl Examples include vinyl ethers such as vinyl ether, unsaturated acid esters such as ethyl acrylate, propyl methacrylate, diethyl maleate, and diptyl fumarate.

The polyurethane resin having a metal sulfonate base in the present invention is a two-component polyol-cured polyurethane resin, and is obtained by the reaction of a polyester polyol having a metal base sulfonate, which is a polyol component, and an isocyanate component.

The polyester polyol having a sulfonic acid metal base consists of a carboxylic acid component without a sulfonic acid metal base, a glycol component, and a dicarboxylic acid component having a sulfonic acid metal base.

Examples of the carboxylic acid component having no sulfonic acid metal base include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and orthophthalic acid; aromatic oxycarboxylic acids such as p-oxybenzoic acid and p-(hydroxyethoxy)benzoic acid; Examples include aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid, and tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid.

Examples of the glycol component include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, polyethylene glycol, trimethylolpropane, and glycerin.

Examples include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. The copolymerization amount of the dicarboxylic acid component having these sulfonic acid metal bases is preferably 0.5 mol% or more, particularly 1 to 50 mol% of the total carboxylic acid components.

Isocyanate components include tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, methylene bis-(4-phenyl isocyanate), hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, xylylene diisocyanate, lysine diisocyanate, dimer acid diisocyanate, isophorone diisocyanate, and methylcyclohexane. -2,4-diisocyanate, 4°4″
A diisocyanate compound such as -methylenebis-(cyclohexyl isocyanate), a low polymer thereof, or an adduct of a diisocyanate compound and a polyol such as trimethylolpropane is used.

The blending ratio of the polyester polyol having a sulfonic acid metal base as a polyol component and the isocyanate component is preferably such that the ratio of the NCO group of the isocyanate to the OH group of the polyol is in the range of 0.5 to 2.

In the present invention, the content of the vinyl copolymer and polyurethane resin in the magnetic layer is 10% of the barium ferrite magnetic powder.
The total amount of both is preferably 10 to 30 parts by weight, and each is preferably 5 to 25 parts by weight.

In the present invention, in addition to vinyl copolymers and polyurethane resins, binders that are commonly used in magnetic recording media, such as vinyl chloride-vinylidene chloride copolymers, cellulose derivatives such as nitrocellulose resin, Acrylic resin, polyvinyl acecool resin, polyvinyl butyral resin, epoxy resin, phenoxy resin, etc. may be used in combination.

As the barium ferrite magnetic powder of the present invention, general 2B
aO・n(Fe1t-xMxO+5-y) (M is Co, Ni, Cu, Zn, Mg, Mn
, In, Ti, Zr, Sn, Ge.

At least one element selected from Nb, V, SbSTaSMo and W, n = 0.8 to 1.2
, x=0°1~5.0, )'= (3-m)x/2, m
represents the average valence of M. ) Magnetobrambite type barium ferrite magnetic powder is preferred. Especially M
are Co5Ni, Zn, and Ti, and those with an average valence m of less than 3 are preferable because they have high saturation magnetization, small temperature changes in coercive force, and sharp anisotropic magnetic field distribution.

As the support of the present invention, for example, a synthetic resin film such as polyethylene terephthalate, polypropylene, polycarbonate, polyamide resin, polyimide resin, etc. is used. The thickness of the support is generally from 3 to ioum, preferably from 5 to 80 am.

In the magnetic recording medium of the present invention, the magnetic layer further includes:
By containing inorganic particles in the magnetic layer, preferably containing inorganic particles having a Mohs hardness of 5 or more,
The abrasive action of the head prevents the head from clogging and improves running durability. Examples of inorganic particles include A2□03 (Mohs hardness: 9), CrzOz (
Mohs hardness 9), Ti(h (Mohs hardness 6.5)
, 5iOz (Mohs hardness: 7), 5nOz (Mohs hardness: 6.5), etc. may be used alone or in combination. The content of inorganic particles is barium ferrite magnetic powder 100
It is usually 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight.

In the magnetic recording medium of the present invention, the magnetic layer further includes:
Known additives such as dispersants, antistatic agents, lubricants, and curing agents may also be used.

As a dispersant, oily or powdered lecithin, carbon number 12-
22 saturated or unsaturated fatty acids, alkali metal salts of the above fatty acids, esters of the above fatty acids or compounds in which some or all of their hydrogen atoms are replaced with fluorine atoms, amides of the above fatty acids, aliphatic amines, higher alcohols, etc. It will be done. The amount of dispersant added is barium ferrite magnetic powder 10
It is usually 0.1 to 10 parts by weight relative to 0 parts by weight.

Antistatic agents include conductive fine powders such as carbon black and carbon black graft polymers, natural surfactants such as saponin, anionic surfactants such as alkylene oxide, glycerin, and grindol, and higher alkyl amines. , quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, cationic surfactants such as phosphonium or sulfoniums, amphoteric surfactants such as amino acids, aminosulfonsanes, sulfuric acid or phosphoric acid esters of amino alcohols, etc. agents, etc.

The amount of antistatic agent added is barium ferrite magnetic powder 10
It is usually 0.1 to 10 parts by weight relative to 0 parts by weight.

As lubricants, saturated or unsaturated fatty acids with 12 to 22 carbon atoms, higher alcohols, monobasic acids and fatty acids with 12 to 20 carbon atoms such as butyl stearate, sorbitan oleate, and monovalent fatty acids with 3 to 22 carbon atoms are used. or esters consisting of polyhydric alcohols, mineral oils, animal and vegetable oils, olefin low polymers, fatty acid amides, silicone oils, modified silicone oils, alkylene oxide adducts of fatty acids, fine graphite powder, fine molybdenum disulfide powder, tetrafluoroethylene. Known lubricants such as fine polymer powder and lubricants for plastics may be mentioned. The amount of lubricant added is usually 0.1 parts by weight per 100 parts by weight of barium ferrite magnetic powder.
~10 parts by weight.

Examples of the curing agent include the above-mentioned bifunctional or higher functional isocyanate compounds. The amount of curing agent added is usually 5 to 40 parts by weight per 100 parts by weight of the binder.

The magnetic recording medium of the present invention can be produced by a conventional method, for example, by kneading magnetic powder, a binder, and an additive with a solvent to produce a magnetic paint, applying this magnetic paint to a support, and then subjecting it to a drying treatment, etc. Manufactured by

There are no particular restrictions on the kneading method, and ordinary kneading machines such as two-roll mills, three-roll mills, ball mills, pebble mills, thoron mills, sand grinders, high-speed impeller dispersers, high-speed stone mills, dispersers, and kneaders can be used.
1. A high-speed mixer, homogenizer, ultrasonic disperser, etc. are used. Moreover, the order of addition of each component can also be set as appropriate.

As solvents added to magnetic paints or diluting solvents during paint application, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone,
Alcohols such as methanol, ethanol, propatool, butanol, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol senoacetate, ethers such as glycol dimethyl ether, glycol monoether, dioxane, tetrahydrofuran, benzene , aromatic hydrocarbons such as toluene and xylene.

The magnetic paint may be applied directly onto the support or via an adhesive layer, etc. Application methods include air doctor coating, blade coating, rod coating, and extrusion coating. , air knife coating, squeeze coating, reverse roll coating, transfer roll coating, clavier coating, kiss coating, cast coating, spray coating, and spin cord.

The thickness of the magnetic layer to be applied is generally 0.000 mm after drying.
The thickness is 5 to 15 μm, preferably 1 to 10 μm.

Drying after coating may be carried out by orienting the magnetic particles in a magnetic field, or may be carried out in a non-oriented state.Furthermore, the surface of the medium may be smoothed by a supercalender treatment, etc., and then dried in an open position, etc. A magnetic recording medium is obtained by curing the medium.

(Example) The present invention will be explained in more detail by showing Examples and Comparative Examples below.

(Reference Example 1) Polymerization was performed using vinyl chloride, hydroxypropyl acrylate, 2-acrylamido-2-methylpropanesulfonic acid Na salt, and allyl glycidyl ether, and (a
) unit 80% by weight, (b) unit 9% by weight, (c) unit 5
A vinyl copolymer having a proportion of 6% by weight and 6% by weight of Q units was obtained.

(Reference Example 2) Polymerization was performed using vinyl chloride, vinyl acetate, 2-hydroxypropyl methacrylate, allyldodecyl sulfosuccinate Na salt, and vinylcyclohexene monooxide, and (a) units were 75% by weight, and (b) units were 7. weight%
A vinyl copolymer containing 3% by weight of (c) units, 5% by weight of (b) units, and 10% by weight of vinyl acetate units was obtained.

(Reference Example 3) After performing a transesterification reaction using dimethyl terephthalate, dimethyl 5-sodium sulfoisophthalate, ethylene glycol, and neopentyl glycol, sebacic acid was added and a li condensation reaction was performed.
mol%, 5-sodium sulfoisophthalic acid 10 mol%
A polyester polyol containing 60 mol% of sebacic acid, 44 mol% of ethylene glycol, and 56 mol% of neopentyl glycol was obtained.

This polyester polyol and diphenylmethane diisocyanate were reacted to obtain a polyurethane resin.

Example 1 A slurry having the following composition was prepared using barium ferrite magnetic powder having the above characteristics, and was dispersed in a sand grinder for 30 minutes.

Magnetic powder 100 parts by weight Vinyl copolymer (Reference Example 1) 8 parts by weight Cyclohexanone 70 parts by weight Methyl ethyl ketone
40 parts by weight glass peas 1
000 parts by weight Next, to the obtained slurry, 10 parts by weight of polyurethane resin (Reference Example 3) Alumina (Two-tone E440) 5 parts by weight Carbon black 5 parts by weight Lecithin
4 parts by weight ethyl stearate
After adding 4 parts by weight of toluene, 100 parts by weight, and 20 parts by weight of methyl ethyl ketone and kneading for 2 hours, 5.7 parts by weight of Coronate (manufactured by Nippon Polyurethane Co., Ltd.) as a hardening agent was added, and the mixture was filtered through a filter with an average particle size of 1 μm. A magnetic paint was prepared.

The obtained magnetic coating material was applied to the surface of a polyethylene terephthalate film having a thickness of 75 μm, and after being oriented in a magnetic field at 4 kOe, it was dried. Furthermore, the surface of the magnetic layer was smoothed using a supercalender device, so that the thickness of the magnetic layer was 4 μm.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 17
20G, the squareness ratio in the thickness direction of the magnetic layer was 0.86, and the gloss was 90%.

Example 2 A magnetic coating film was produced in the same manner as in Example 1 using barium ferrite magnetic powder having the above characteristics.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 17
20G, the squareness ratio in the thickness direction of the magnetic layer was 0.76, and the gloss was 94%.

Example 3 A slurry with the following composition was prepared using the same barium ferrite magnetic powder as in Example 1, and the slurry was ground in a sand grinder for 30 minutes.
Dispersed for 0 minutes.

Magnetic powder 100 parts by weight Vinyl copolymer (Reference Example 2) 10 parts by weight Methyl ethyl ketone 40 parts by weight Glass beads
1000 parts by weight Next, to the obtained slurry, 8 parts by weight of polyurethane resin (Reference Example 3) Alumina (Two-tone E440) 5 parts by weight Carbon black 5 parts by weight Lecithin
4 parts by weight methyl stearate
After adding 4 parts by weight of toluene, 100 parts by weight, and 20 parts by weight of methyl ethyl ketone and kneading for 2 hours, 5.7 parts by weight of Coronate (manufactured by Nippon Polyurethane Co., Ltd.) as a hardening agent was added, and the average particle size was 1.
The mixture was filtered through a μm filter to prepare a magnetic paint.

The obtained magnetic coating material was applied to the surface of a polyethylene terephthalate film having a thickness of 75 ttm, and after being oriented in a magnetic field at 4 kOe, it was dried. Furthermore, the surface of the magnetic layer was smoothed using a super calendar device, and the thickness of the magnetic layer was reduced to 4 μm.
I made it.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 17
50G, the squareness ratio in the thickness direction of the magnetic layer was 0.87, and the gloss was 91%.

Example 4 A magnetic coating film was produced in the same manner as in Example 3 using the same barium ferrite magnetic powder as in Example 2.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 17
40G, the squareness ratio in the thickness direction of the magnetic layer was 0.77, and the gloss was 94%.

Example 5 A slurry with the following composition was prepared using the same barium ferrite magnetic powder as in Example 1, and the slurry was ground in a sand grinder for 6 hours.
Dispersed for 0 minutes.

Magnetic powder 100 parts by weight Vinyl copolymer (Reference Example 1) 8 parts by weight Cyclohexanone 80 parts by weight Methyl ethyl ketone
50 parts by weight glass beads 8
00 parts by weight Next, to the obtained slurry, 12 parts by weight of polyurethane resin (Reference Example 3) Alumina (Two-tone E440) 5 parts by weight Carbon black 5 parts by weight Lecithin
2 parts by weight methyl stearate
After adding 2 parts by weight of toluene, 100 parts by weight, and 10 parts by weight of methyl ethyl ketone and kneading for 2 hours, 5.7 parts by weight of Coronate (manufactured by Nippon Polyurethane Co., Ltd.) as a hardening agent was added, and the mixture was filtered through a filter with an average particle size of 1 μm. A magnetic paint was prepared.

The obtained magnetic coating material was applied to the surface of a polyethylene terephthalate film having a thickness of 75 pm, oriented in a magnetic field at 4 kOe, and then dried. Furthermore, the surface of the magnetic layer was smoothed using a supercalender device, so that the thickness of the magnetic layer was 4 μm.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 17
30G, the squareness ratio in the thickness direction of the magnetic layer was 0.85, and the gloss was 92%.

Comparative Example 1 In Example 3, the vinyl copolymer (Reference Example 2) was replaced with a vinyl chloride-vinyl acetate copolymer (VAGH: manufactured by UCC), and the polyurethane resin (Reference Example 3) was replaced with polyurethane resin. A coating film was prepared in the same manner as in Example 3, except that the coating material was changed to 3022 (manufactured by Nippon Polyurethane Co., Ltd.).

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 14
50G, the squareness ratio in the thickness direction of the magnetic layer was 0.75, and the gloss was 41%.

Comparative Example 2 A coating film was produced in the same manner as in Example 1, except that the polyurethane resin (Reference Example 3) was changed to Tuboran 3022 (manufactured by Nippon Polyurethane Co., Ltd.).

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 15
20G, the squareness ratio in the thickness direction of the magnetic layer was 0.76, and the gloss was 71%.

Comparative Example 3 In Example 1, the vinyl copolymer (Reference Example 1) was replaced with vinyl chloride-vinyl acetate copolymer (VA″GH: UCC
A coating film was prepared in the same manner as in Example 1, except that the coating material was changed to 1.

As a result of measuring the magnetic properties of the obtained coating film, the magnetic flux density was 15
50G, the squareness ratio in the thickness direction of the magnetic layer was 0.76, and the gloss was 78%.

Claims (1)

[Scope of Claims] A magnetic recording medium in which a magnetic layer containing barium ferrite magnetic powder is provided on a support, in which the magnetic layer contains (i) a vinyl copolymer consisting of each of the following structural units; ) a vinyl chloride unit, (b) a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group, (c) a monovalent organic group whose side chain is a -SO_3M group or a -SO_3M group (M in the formula is a hydrogen atom or a metal atom), (d) a vinyl monomer unit having an epoxy group in the side chain, and (ii) a polyurethane resin having a sulfonic acid metal base. A magnetic recording medium characterized by: