JPH08124143A - Magnetic recording media - Google Patents

Abstract

(57) [Summary] [Object] To provide a magnetic recording medium suitable for high-density recording by improving dispersibility and magnetostatic characteristics without impairing durability. [Structure] A magnetic layer is formed on a non-magnetic support and is composed of a coating film of a magnetic paint mainly composed of a magnetic powder and a binder, and has a polyoxyethylene group and a hydroxyl group as a dispersant in the magnetic layer. An oligomer mainly composed of acrylic acid ester and / or methacrylic acid ester having a molecular weight of 1000 to 5000 g / mol is added, and an isocyanate compound is used as a curing agent. The content of the oligomer is 0.
It is preferably 5 to 10 parts by weight. Further, it is preferable to use an organic metal salt together with the above-mentioned oligomer as a charge donor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium having a magnetic layer composed of a magnetic powder and a binder on a non-magnetic support, and particularly to an additive such as a dispersant and a curing agent. Regarding improvement.

[0002]

2. Description of the Related Art In the field of magnetic recording, particularly in a VTR (video tape recorder) or the like, in order to improve image quality,
Higher density recording is required. Along with this improvement in image quality, iron or a metal material mainly containing iron has come to be used in place of the iron oxide-based material conventionally used as magnetic powder for magnetic recording media and the like. Ferromagnetic metal fine particles, iron oxide or iron oxohydroxide, or Co, N composed of iron or a metal material mainly containing iron
It is produced by reducing iron hydroxide, iron oxohydroxide, or the like containing a metal other than iron such as i, Cr, Mn, Cu, Zn, and Ti with hydrogen gas. These ferromagnetic metal particles are
It has magnetic properties superior to those of conventional iron oxide-based ferromagnetic powder.

However, since the ferromagnetic metal fine particles have high surface activity and are modified with the above metals other than iron, the surface acidity or basicity may become strong, and they are made into a coating material together with a binder. However, when cyclohexanone or the like is used as the organic solvent, a modified product may be generated, which may hinder the adsorption of the binder to the magnetic powder and deteriorate the dispersibility, electrostatic properties and durability. Such properties tend to become stronger as the magnetic powder is subdivided along with the reduction in noise of the magnetic recording medium. Therefore, when the above-mentioned ferromagnetic metal fine particles are used as magnetic powder for a magnetic recording medium, a ball mill may be used during the process of forming a coating material in combination with a resin or an organic solvent that produces a modified product such as cyclohexanone. As a result, a modified product such as cyclohexanone is produced during mixing and dispersion, or during the kneading of the magnetic powder and the resin as a pretreatment, which causes problems such as deterioration of dispersibility or deterioration of magnetostatic characteristics.

To solve this problem, the following method has been proposed.

That is, (1) In order to control the generation of a modified compound such as an organic solvent on the surface of the ferromagnetic metal fine particles, the surface activity is controlled by attaching water to the surface of the ferromagnetic metal fine particles. Or (2) a method of coating the surface of the ferromagnetic metal fine particles with a low activity Si element or the like.

However, in the methods (1) and (2), the adsorption amount of the resin may be reduced,
As a result, the dispersibility originally possessed by the resin may be deteriorated and the dispersion stability may be deteriorated, and it cannot be said that the method is always satisfactory.

In addition to the above methods (1) and (2),
(3) A method of coating the surface of ferromagnetic metal fine particles with a low-molecular weight organic substance or oligomer to control contact with an organic solvent is also known. A magnetic coating having high dispersibility is obtained, and calendering is performed as a surface treatment. The efficiency of the magnetic recording medium is improved and a high output magnetic recording medium can be obtained, but it is considered that the durability of the magnetic recording medium is likely to be deteriorated because the magnetic layer is easily plasticized.

[0008]

Therefore, the present invention has been proposed in view of such circumstances, and aims to improve the dispersibility and magnetostatic characteristics without impairing the durability and to achieve high density recording. It is an object of the present invention to provide a magnetic recording medium suitable for

[0009]

Means for Solving the Problems The inventors of the present invention have earnestly studied that the above-mentioned objects were achieved, and as a result, as the dispersant, an acrylic ester or methacrylic ester having a polyoxyethylene group and a hydroxyl group was mainly used. It has been found that by using an oligomer to be used, and by using an isocyanate compound as a curing agent when preparing a magnetic coating, it is possible to exhibit the original dispersion ability of the resin while ensuring good durability. Has been completed.

That is, the magnetic recording medium of the present invention is a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed of a coating film of a magnetic coating material mainly composed of magnetic powder and a binder. The layer contains an oligomer mainly composed of acrylic acid ester and / or methacrylic acid ester having a polyoxyethylene group and a hydroxyl group and having a molecular weight of 1000 to 5000 g / mol as a dispersant, and an isocyanate compound as a curing agent for the above magnetic coating material. Is added.

In the magnetic recording medium of the present invention, as an oligomer mainly composed of an acrylic acid ester and / or a methacrylic acid ester having a polyoxyethylene group and a hydroxyl group and having a molecular weight of 1000 to 5000 g / mol, which is used as a dispersant, the following ( Those having a structure represented by the formula (1) can be used.

[0012]

Embedded image

However, in the above formula (1), R _1, R _2, R
_3, R ₅ are each —H, —CH ₃ , —C ₆ H ₅ (aromatic ring), —NH ₂ , —COOH, —R—SH (R represents an alkyl group or an aromatic ring. The same applies hereinafter. ), -Cl, -R
Cl represents a side chain such as Cl, and R ₄ represents —R—OH (which may hold a plurality of —OH).

The alkyl group R may be a linear or branched alkyl group, or may have a polar group.

Further, these R _1, R _2, R _{3 and} R ₅ are
Branches become -COOR, wherein _{R 1, R 2, R 3} , R 5
Or the above R _1, R _2, R
_The monomer units represented by _3, R _{4 and} R ₅ may be repeated.

Further, x, y and z represent respective polymerization ratios.

Here, the above polyoxyethylene group (--C
The repeating unit (H ₂ CH ₂ —O—) behaves as if it were a crown ether, and is adsorbed at the active site of the ferromagnetic metal powder in the coordination field formed by the polyoxyethylene group.

The number of repeating unit units in this polyoxyethylene structure is preferably 2 to 23. If this number of unit units is too large, it will be difficult to dissolve in an organic solvent, and if it is too small, the solubility will improve but the action as a functional group will decrease.

Commercially available dispersants having such a polyoxyethylene structure include, for example, Plysurf A207H (manufactured by Dai-ichi Kogyo Co., Ltd.), which also forms a coordination field similar to that described above. Acts as a dispersant. However, since it has no crosslinking group in the magnetic layer, it acts as a plasticizer and reduces durability.

On the other hand, when an oligomer mainly composed of an acrylic ester and / or a methacrylic ester having a polyoxyethylene group and a hydroxyl group is used, a hydroxyl group is used as a functional group reactive with an isocyanate group. Therefore, it is crosslinked in the magnetic layer, plasticization is prevented, and deterioration of durability is prevented. Further, the hydroxyl group is
Depending on its polarity, it can be adsorbed on the active sites of the ferromagnetic metal powder, and can reduce the transformation of the ketone solvent.

On the other hand, as the above-mentioned isocyanate compound, in order to realize three-dimensional crosslinking, a binder resin, an oligomer having the above-mentioned polyoxyethylene structure and a hydroxyl group, etc., preferably three or more in one molecule. It is better to have an isocyanate group.

As a curing agent satisfying these conditions,
For example tolylene diisocyanate (TDI), 4,4 '
-Diphenylmethane diisocyanate (MDI), hexameethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), etc., or trimers derived therefrom, such as trimers, and 3,3,3-trimethylolpropane (TMP) Compounds having a structure reacted with a polyol compound such as

Specifically, as the HDI trimer, Coronate EH (manufactured by Nippon Polyurethane Co., Ltd., the same applies hereinafter), Coronate HL as the compound of TMP and HDI, Coronate L as the compound of TMP and TDI, etc. There is.

The amount of these isocyanate compounds added is usually 10 to 30% by weight in terms of the ratio to the binder so that the number of moles of isocyanate groups is equal to or more than the number of moles of hydroxyl groups contained in the binder resin. It is preferable.

Further, by using an organic metal salt in combination with an oligomer mainly composed of an acrylic acid ester and / or a methacrylic acid ester having a polyoxyethylene group and a hydroxyl group, the organic metal salt can be converted into a polyoxyethylene group and a hydroxyl group. It has a dissociation property and can be positively charged to enhance the adsorption ability (affinity) of the negatively chargeable resin to the magnetic powder. In this way, the polarity of the surface of the magnetic powder can be increased, and as the interaction with the polar group or site of the binder resin, the field of dipole-dipole interaction, hydrogen bondability, acid / base interaction is strengthened. The dispersibility of the magnetic powder can be increased.

The amount of the oligomer mainly composed of acrylic acid ester and / or methacrylic acid ester having a polyoxyethylene group and a hydroxyl group is 100
It is preferably 0.2 to 10 parts by weight with respect to parts by weight. If the addition amount of the oligomer is less than the lower limit, it becomes difficult to sufficiently secure the effect of addition. On the contrary, if it exceeds the upper limit, the amount of non-magnetic substance components other than the binder resin is increased, which leads to deterioration of magnetostatic properties. There is a fear.

The content of the above hydroxyl group is preferably 2 to 5 mmol / g. The content of this hydroxyl group is 2
If it is less than 1 mol / g, the ability to adsorb to the active sites on the surface of the ferromagnetic powder decreases, and the reactivity with the isocyanate compound as a curing agent decreases, causing plasticization of the magnetic layer and This causes a decrease in the mechanical strength of the film. On the contrary, when the content of the hydroxyl group is more than 5 mmol / g, the solubility in the organic solvent is lowered, and the curing as the dispersant cannot be expected. Examples of the organic metal salt include metal salts of fatty acids such as naphthenic acid, octenoic acid, oleic acid, stearic acid, isostearic acid, and lauric acid, metal salts of sulfosuccinic acid esters, oil-soluble sulfonic acid ester metal salts, and phosphoric acid. Examples thereof include ester metal salts, metal salts such as abietic acid, aromatic carboxylic acid metal salts, aromatic sulfonic acid metal salts, and the like.

The amount of the organic metal salt as the charge-donating agent added is 1 to 100 parts by weight of the magnetic powder.
It is preferably 0.001 part by weight. If the amount of the organic metal salt added is less than the above lower limit, the effect as positive charging cannot be expected, and if it is more than the above upper limit, the polarity in the organic solvent tends to increase, and the bond adsorbed depending on the polarity. It reduces the interaction of the agent resin with the surface of the magnetic powder.

The magnetic recording medium to which the present invention is applied includes a so-called coating type magnetic recording medium in which a magnetic coating film is formed as a magnetic layer by coating a magnetic coating on the surface of a non-magnetic support.

In the above-mentioned coating type magnetic recording medium, any conventionally known magnetic powder or the like can be used as the non-magnetic support or the magnetic coating film, and the magnetic powder is not limited in any way.

As a specific example, as magnetic powders, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and Fe can be used.
Beltride compound with ₃ O ₄ , γ-Fe ₂ O containing Co
₃ , Co-containing Fe ₃ O _4, γ-Fe ₂ O containing Co
1 in CrO _{2m , a} beltride compound of ₃ and Fe ₃ O _4.
Seeds or higher metallic elements (eg Te, Sb, Fe,
Bi, etc.)-Containing oxides, metals such as Fe, Co and Ni, Fe-Co, Fe-Ni, Fe-Al, Fe-Ni
-Al, Fe-Al-P, Fe-Ni-Si-Al, F
e-Ni-Si-Al-Mn, Fe-Mn-Zn, Fe
-Ni-Zn, Co-Ni, Co-P, Fe-Co-N
i, Fe-Co-Ni-Cr, Fe-Co-Ni-P,
Fe-Co-B, Fe-Co-Cr-B, Mn-Bi,
Examples thereof include alloys such as Mn-Al and Fe-Co-V, iron nitride, iron carbide and the like.

Of course, even if a light metal element such as Al, Si, P or B is added in an appropriate amount for the purpose of preventing sintering during reduction or maintaining the shape, the effect of the present invention is not hindered.

Examples of the thermoplastic resin as the resin binder include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic. Acid ester-vinylidene chloride copolymer,
Methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyvinyl Butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, synthetic rubber and the like can be mentioned.

As the thermosetting resin, phenol resin,
Examples thereof include epoxy resin and silicone resin.

The amount of these binder resins used in the magnetic layer is 1 to 200 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the magnetic powder. If the amount of the binder resin used is too large, the ratio of the magnetic powder in the magnetic layer relatively decreases, resulting in a decrease in output. On the other hand, if the amount of the binder resin used is too small, the mechanical strength of the magnetic layer decreases, and the running durability of the magnetic medium decreases.

In the present invention, if necessary, a lubricant,
Nonmagnetic reinforcing particles, conductive particles, surfactants and the like can be contained in the above magnetic layer, and their compounding ratio and the like are also set according to the case of an ordinary magnetic recording medium.

As the above-mentioned lubricant, graphite, molybdenum disulfide, silicone oil, fatty acid having 10 to 2 carbon atoms, fatty acid ester consisting of this and alcohol having 2 to 26 carbon atoms, terpene compound, and these It is possible to use oligomers of

Examples of the nonmagnetic reinforcing particles include aluminum oxide, chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride and the like.

The amount of the non-magnetic reinforcing particles used is 20 parts by weight, preferably 10 parts by weight, per 100 parts by weight of the magnetic powder.
It is less than or equal to parts by weight. The average particle size of the non-magnetic reinforcing particles is 1.0 μm or less, preferably 0.5 μm or less.

As the conductive particles, carbon black, graphite and other metal particles can be used.

As the above-mentioned surfactant, amphoteric ones such as nonionic, anionic and cationic can be used.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, bi-based resins and polyimides. And a polymeric material typified by polycarbonates, or a support formed of metal, glass, ceramics, or the like.

To form a magnetic layer on these non-magnetic supports, the above-mentioned magnetic layer constituting material is made into a coating material, which is applied onto the above-mentioned non-magnetic support and dried to form a coating material. In this case, the solvent used is, for example, acetone,
Methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanone, alcohol solvents such as methanol, ethanol, propanol, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester type solvents such as ethylene glycol acetate, ether type solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, carbon tetrachloride, chloroform and chlorobenzene. It is possible to use halogenated hydrocarbon solvents such as

The dispersion / kneading for preparing the above-mentioned coating material is carried out, for example, by a roll mill, a ball mill, a sand mill,
An agitator, kneader, extruder, homogenizer, ultrasonic disperser, etc. are used.

Further, to apply the coating material thus prepared on the above non-magnetic support, a gravure coater, a knife coater, a wire bar coater, a doctor blade coater, a reverse roll coater, a dipping coater, an air knife coater, a die coater is used. And the like are used.

[0046]

By using an oligomer mainly composed of an acrylic ester or methacrylic ester having a polyoxyethylene group and a hydroxyl group as a dispersant constituting the magnetic layer, and by using an isocyanate compound in combination as a curing agent, an isocyanate compound is obtained. Since a hydroxyl group is introduced as a functional group reactive with the group, crosslinking occurs in the magnetic layer, plasticization is prevented, and good durability is obtained.

[0047]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, an oligomer used as a dispersant was synthesized prior to the formation of the magnetic layer.

<Synthesis of Oligomer> As a monomer having an oxyethylene group, CH ₂ ═C (CH ₃ ) COO (C
_{H 2 CH 2 O) 4 CH} 3 (M-40G) with which the methacrylic acid 2-hydroxyethyl CH ₂ = C (C
H ₃ ) COOCH ₂ CH ₂ OH was added and weighed so that the molar ratio was 20%: 80%, and azobisisobutyronitrile ((CH ₃ ) ₂ ( CH) CN) ₂ was added.

Then, about 20 times as much solvent (toluene) was added thereto, and then bubbling with dry nitrogen gas was carried out.
The tube was sealed under the nitrogen atmosphere and a polymerization reaction was carried out at a temperature of 80 ° C. for about 24 hours.

After that, the product was purified by n-hexane, the solvent was completely removed, and the product was stored.

The weight average molecular weight of the obtained oligomer is
It was about 2100 g / mol as measured by high performance liquid chromatography manufactured by Showa Denko KK.

Next, a magnetic tape was produced using the oligomer synthesized as described above. That is, first, a commercially available magnetic powder for a magnetic recording medium was prepared. The magnetic characteristics and powder characteristics of this magnetic powder for magnetic recording media are as follows.

Saturation magnetization = 125 Am ² / kg Squareness ratio = 0.49 Coercive force = 119 kA / m Specific surface area = 53 m ² / g Needle ratio = 12 The above magnetic characteristics are those manufactured by Toei Industry Co., Ltd. The specific surface area was measured by a BET single point method manufactured by Shimadzu Corporation using a sample vibration type magnetometer. The acicular ratio was an average value of 100 points randomly selected by observation with a transmission microscope.

Using this sample powder, a binder resin, carbon, Al ₂ O ₃ as an additive, and the above-mentioned oligomer, the mixture was kneaded and dispersed through the following coating composition to form a coating, and an isocyanate compound (product (Name: Coronate L, manufactured by Nippon Polyurethane Company) was added to obtain a magnetic coating material.

Then, this magnetic paint was applied to a 14 μm thick PE.
It was coated on a T (polyethylene terephthalate) film, oriented and dried.

Subsequently, calendering was carried out as a surface treatment step, and further curing was carried out in a curing oven at a temperature of 60 ° C. for 24 hours to obtain a sample tape.

<Coating composition> 100 parts by weight of ferromagnetic metal powder Polyester polyurethane resin (containing -SO ₃ Na) 10 parts by weight of the polyvinyl chloride resin (-SO ₃ Na content) 10 parts by weight Carbon (average particle size 20 nm) 3 parts by weight Al ₂ O ₃ (average particle size 500 nm) 2 parts by weight Methacrylate ester oligomer 5 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight As described above The prepared sample tape was examined for dispersibility, magnetic properties and durability.

The dispersibility was evaluated by measuring the glossiness with a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.). In the measurement, the incident angle of the light beam was set to 45 degrees, and the gloss of the reference plate having the standard surface was set to 100%, and the relative value was displayed (JI
According to S-8741. ).

The magnetic characteristics were measured with a sample vibrating magnetometer.

The durability was evaluated by sliding the tape surface with a cotton swab soaked with methyl ethyl ketone and measuring the number of times until the base film was visible as the solvent resistance. here,
The larger the number of slides, the better the crosslinkability, the less plasticity, and the better the durability.

The results are shown in Table 1 below.

[0063]

[Table 1]

Example 2 A monomer having an oxyethylene group (M-40G) and a monomer having a hydroxyl group (2-hydroxyethyl methacrylate) similar to those in Example 1 were used, and the charging amount thereof was half that of Example 1. In the same manner as in Example 1 except for the above, an oligomer was synthesized.

The weight average molecular weight of the resulting oligomer was
It was about 1200 g / mol.

Then, the oligomer used in Example 1 was replaced with the above-synthesized oligomer, and a sample tape was prepared by the same composition and process as in Example 1 except for the above.

Then, the dispersibility, the magnetic characteristics and the durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Example 3 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as those used in Example 1 were used, and the charged amounts of these monomers were the same as those in Example 1. Oligomer was synthesized in the same manner as in Example 1 except for doubling.

The weight average molecular weight of the obtained oligomer was
It was about 4500 g / mol.

Then, the oligomer used in Example 1 was replaced with the oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1, to prepare a sample tape.

Then, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Examples 4 to 6 0.5 parts by weight, 2 parts by weight, and 10 parts by weight of the ligomers synthesized in the above Example 1 were used, and the other components had the same composition and the same process as in Example 1 to prepare sample tapes. did.

Then, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Example 7 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as in Example 1 were used, and the charged amounts thereof were 40% and 60, respectively. %, And an oligomer was synthesized in the same manner as in Example 1 except for the above.

The weight average molecular weight of the resulting oligomer was
It was about 2000 g / mol.

Then, the oligomer used in Example 1 was changed to the oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Then, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Example 8 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as in Example 1 were used, and the charged amounts thereof were 50% and 50, respectively. %, And an oligomer was synthesized in the same manner as in Example 1 except for the above.

The weight average molecular weight of the resulting oligomer is
It was about 2200 g / mol.

Then, the oligomer used in Example 1 was changed to the above-described oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Then, the dispersibility, magnetic properties and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Examples 9 to 12 Add 0.001 parts by weight, 0.01 parts by weight, 0.1 parts by weight, and 1 part by weight of Zr octylate as an organometallic salt compound in the composition of Example 1 above, and others. A sample tape was prepared in the same composition and process as in Example 1.

Therefore, the dispersibility, the magnetic characteristics and the durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 1 A sample tape was prepared in the same composition and process as in Example 1 except that polyoxyethylene and a hydroxyl group oligomer were not added in the composition of Example 1 above.

Then, the dispersibility, magnetic properties and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 2 A sample tape was prepared in the same composition and process as in Example 1 except that Coronate L was not added as a curing agent in the composition of Example 1 above.

Then, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 3 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as those used in Example 1 were used, and the charging amounts thereof were set to those in Example 1 The oligomer was synthesized in the same manner as in Example 1 except for / 4 times.

The weight average molecular weight of the obtained oligomer was
It was about 600 g / mol.

Then, the oligomer used in Example 1 was changed to the above-described oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Therefore, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 4 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as those used in Example 1 were used, and the charged amounts of these monomers were the same as those in Example 1. An oligomer was synthesized in the same manner as in Example 1 except that the number was doubled.

The weight average molecular weight of the obtained oligomer was
It was about 9800 g / mol.

Then, the oligomer used in Example 1 was changed to the oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Then, the dispersibility, magnetic properties and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Examples 5 and 6 Sample tapes were prepared in the same composition and process as in Example 1 except that the oligomers synthesized in Example 1 were 0.1 parts by weight and 20 parts by weight, respectively.

Therefore, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 7 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as in Example 1 were used, and the charged amounts thereof were 70% and 30, respectively. %, And an oligomer was synthesized in the same manner as in Example 1 except for the above.

The weight average molecular weight of the obtained oligomer was
It was about 2400 g / mol.

Then, the oligomer used in Example 1 was changed to the above-described oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Then, the dispersibility, magnetic properties and durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

Comparative Example 8 The same oxyethylene group-containing monomer (M-40G) and hydroxyl group-containing monomer (2-hydroxyethyl methacrylate) as in Example 1 were used, and the charged amounts thereof were 10% and 90%, respectively. %, And an oligomer was synthesized in the same manner as in Example 1 except for the above.

The weight average molecular weight of the obtained oligomer was
It was about 1500 g / mol.

Then, the oligomer used in Example 1 was replaced with the oligomer synthesized in this Example, and the other components were the same in composition and in the same process as in Example 1 to prepare a sample tape.

Therefore, the dispersibility, magnetic characteristics and durability of the obtained sample tape were examined as described above, and the results are shown in Table 1 above.

Comparative Example 9 3 parts by weight of Zr octylate was added as the organometallic salt compound in the composition of Example 1 above, and the other components were the same as in Example 1,
A sample tape was produced in the same process.

Then, the dispersibility, the magnetic characteristics and the durability of the obtained sample tape were examined as described above, and the results are also shown in Table 1 above.

From the above results, as shown in Table 1, comparing the presence or absence of the oligomer having an oxyethylene group and a hydroxyl group with that of Example 1 and Comparative Example 1, an oligomer having an oxyethylene group and a hydroxyl group was added. In Example 1, it was found that the dispersibility (gloss 45 °) and the magnetostatic property were significantly improved.

Further, comparing the presence or absence of the addition of the isocyanate compound curing agent in Example 1 and Example 2, the solvent resistance was significantly lower in Comparative Example 2 in which the isocyanate compound curing agent was not added.

From the above, when an oligomer having an oxyethylene group and a hydroxyl group is used, the dispersibility and the magnetostatic property can be improved without impairing the solvent resistance by using the curing agent of the isocyanate compound together. I understood.

Here, in FIG. 1, the gloss 4 against the weight average molecular weight of the oligomer having an oxyethylene group and a hydroxyl group is shown.
The relationship between 5 ° (%) and solvent resistance is shown.

As is apparent from FIG. 1, the weight average molecular weight of the oligomer having an oxyethylene group and a hydroxyl group was 50.
When it is less than 00 g / mol, the dispersibility is improved, and it acts as a plasticizer before the curing accelerating step to improve the efficiency of the calendar treatment in the surface treatment step, improve the filling rate of the magnetic powder, and harden it. Solvent resistance was improved due to crosslinking by the curing agent of the isocyanate compound in the process.

However, when the weight average molecular weight of the oligomer having an oxyethylene group and a hydroxyl group is less than 1000, the number of crosslinking points with the isocyanate compound is decreased, so that the solvent resistance is deteriorated, and the weight average molecular weight of the oligomer is If it is more than 5000 g / mol, dispersibility deteriorates,
Also, the deterioration of the uniformity of the resin content of the coating film due to the poor dispersibility deteriorated the durability.

Thus, in a magnetic recording medium in which the above-mentioned oligomer having an oxyethylene group and a hydroxyl group is added and an isocyanate compound is used as a curing agent, when the weight average molecular weight of the above-mentioned oligomer is 1000 to 5000 g / mol. It was found that the dispersibility and magnetostatic properties were improved without impairing the solvent resistance.

In addition, in a magnetic recording medium in which the oligomer having an oxyethylene group and a hydroxyl group is added to FIG. 2 and an isocyanate compound is used as a curing agent, the addition amount of the oligomer is 45 ° (%) and the solvent resistance is high. Showed the effect on.

As shown in FIG. 2, if the amount of the oxyethylene group- and hydroxyl group-containing oligomer added is 0.5 parts by weight or more, the dispersibility, electrostatic characteristics and solvent resistance will start to improve.
When the amount is more than 10 parts by weight, the amount of the binder resin adsorbed on the magnetic powder begins to be impaired, and the deterioration of the uniformity due to the deterioration of the uniformity of the resin content of the coating film due to the poor dispersibility was observed.

As a result, in the magnetic recording medium in which the oligomer having an oxyethylene group and the hydroxyl group is added and the isocyanate compound is used as a curing agent, the addition amount of the oligomer is 0.5 to 10 parts by weight. In addition, it was found that the dispersibility and magnetostatic properties are improved without impairing the solvent resistance.

Furthermore, in a magnetic recording medium in which the oligomer having an oxyethylene group and a hydroxyl group is added to FIG. 3 and an isocyanate compound is used as a curing agent, the gloss is 45 ° with respect to the content of the hydroxyl group of the oligomer.
(%), Showing the effect on solvent resistance.

As shown in FIG. 3, when the content of the hydroxyl group in the oligomer is up to 3 mmol / g, the adsorptivity on the surface of the magnetic powder is improved with the increase of the hydroxyl group, and the crosslinking point of the isocyanate compound with the curing material is increased. 45 to increase
(%), Solvent resistance is improved, and when the content of hydroxyl groups in the oligomer is more than 5 mmol / g, the solubility in an organic solvent at the time of forming a coating becomes poor and the gloss 45 ° deteriorates. It has been found that the mechanical properties of the coating film are deteriorated due to poor dispersibility in the same manner as described above.

Therefore, in the magnetic recording medium in which the oligomer having an oxyethylene group and a hydroxyl group is added and the isocyanate compound is used as a curing agent, the content of the hydroxyl group in the oligomer is 2 to 5 mmol / g. It was found that the dispersibility and magnetostatic properties were improved without impairing the solvent resistance.

FIG. 4 shows that in the magnetic recording medium in which the above-mentioned oligomer having an oxyethylene group and a hydroxyl group is added and an isocyanate compound is used as a curing agent, the gloss is 45 ° with respect to the addition amount of octylic acid Zr as an organic metal salt.
It is a figure which shows (%) and solvent resistance.

As shown in FIG. 4, when the amount of Zr octylate added is 0.001 part by weight or more, the positive charge starts to increase, the surface activity of the magnetic powder is increased, and the solvent resistance is not impaired. Gloss 45 ° (%), improving the magnetostatic property, and when it is more than 1 part by weight, it starts to act with the binder resin in the organic solvent in the magnetic paint to inhibit the adsorption to the magnetic powder and lower the dispersibility. It has been found that since it does not have a crosslinking group, it acts as a plasticizer and reduces solvent resistance.

From the above, in the magnetic recording medium in which the oligomer having an oxyethylene group and the hydroxyl group is added and the isocyanate compound is used as the curing agent, the addition amount of the organic metal salt should be 0.001 to 1 part by weight or less. It was found that, for example, the dispersibility and magnetostatic properties were improved without affecting the solvent resistance.

[0124]

As is apparent from the above description, the conventional oligomer dispersant plasticizes the magnetic coating film and deteriorates the physical properties of the coating film, but in the present invention, it has an oxyethylene group and a hydroxyl group. By adding an oligomer and using an isocyanate compound as a curing agent, and by using these together with an organic metal salt, the action as a conventional dispersant acting on the surface of magnetic powder and the increase of calendar surface treatment efficiency Further, since the curability is improved by having a crosslinking group, a magnetic coating film having excellent dispersibility can be obtained without lowering the mechanical strength of the magnetic coating film.

Therefore, according to the present invention, it is possible to provide a high dispersion coating type magnetic recording medium suitable for high density recording.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a weight average molecular weight of an oligomer having an oxyethylene group and a hydroxyl group, a gloss of 45 ° (%), and solvent resistance.

FIG. 2 is a characteristic diagram showing a relationship between an addition amount of an oligomer having an oxyethylene group and a hydroxyl group, gloss 45 ° (%), and solvent resistance.

FIG. 3 is a characteristic diagram showing a relationship between a hydroxyl group content in an oligomer having an oxyethylene group and a hydroxyl group, gloss 45 ° (%), and solvent resistance.

FIG. 4 is a characteristic diagram showing the relationship between the addition amount of an organic metal salt, gloss 45 ° (%), and solvent resistance.

Claims (5)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer formed of a coating film of a magnetic paint mainly comprising magnetic powder and a binder, wherein polyoxy is used as a dispersant in the magnetic layer. Characterized by containing an oligomer mainly composed of an acrylic acid ester and / or a methacrylic acid ester having an ethylene group and a hydroxyl group and having a molecular weight of 1000 to 5000 g / mol, and an isocyanate compound being added as a curing agent for the above magnetic paint. And a magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the content of the oligomer is 0.5 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder. 3. The content of the hydroxyl group is 2 to 5 mmol / g.
The magnetic recording medium according to claim 1, wherein 4. The magnetic recording medium according to claim 1, wherein an organic metal salt is used together with the oligomer as a charge donor. 5. The magnetic recording medium according to claim 4, wherein the content of the organic metal salt is 1 to 0.001 part by weight based on 100 parts by weight of the magnetic powder.