JPH06162476A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having improved electro-magnetic transducing characteristics and durability by investigating a binder giving favorable effects on the dispersibility of magnetic powder and the mechanical strength of a magnetic layer. CONSTITUTION:An alkyl (meth) acrylate polymer having a carboxyl group at one terminal of each molecule and an org. compd. having a lower mol.wt. than the polymer having a polar group at one terminal of each molecule are used as a binder for magnetic powder and a magnetic recording medium is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape having a magnetic layer containing a magnetic powder and a binder on a non-magnetic support,
The present invention relates to a magnetic recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art In general, a magnetic recording medium of this type comprises a non-magnetic support such as a polyester film, a magnetic powder,
A magnetic layer is formed by applying a magnetic coating material containing a binder, an organic solvent, and various additives as necessary, and drying it to form a magnetic layer. In order to exhibit high electrical characteristics, magnetic powder in the magnetic layer is used. Is desired to have good dispersibility, and the magnetic layer is required to have excellent mechanical properties in terms of durability.

Conventionally, as a binder for the magnetic layer in such a magnetic recording medium, polyurethane resin, vinyl chloride resin, fibrin resin, butyral resin, acetal resin, polyester resin, etc. have been used. It is widely used, and among them, polyurethane-based resins are widely used as those capable of imparting excellent mechanical properties to the magnetic layer. However, ordinary polyurethane-based resins have excellent mechanical properties, but on the other hand, they have a low ability to disperse magnetic powder, and thus have a drawback that electrical properties of a magnetic recording medium become insufficient.

Therefore, in recent years, for example, JP-A-55-38693, JP-A-57-92422 and 59-59.
As disclosed in respective publications such as -30235,
As a binder, a resin containing a polar group such as a hydroxyl group is used together with the above polyurethane-based resin, or a polar group such as a carboxyl group, a sulfonic acid group, a phosphoric acid group, a tertiary amino group, or a salt thereof in the main chain. A means for improving the dispersibility of the magnetic powder has been adopted by using a polyurethane resin having a group introduced therein.

[0005]

However, with the recent technical progress, it has been strongly demanded to increase the recording density and reliability of the magnetic recording medium. As described above, the polyurethane-based binder is used as the binder. Means such as the combined use of a resin and a resin containing a polar group, or the use of a polyurethane-based resin having various polar groups introduced is no longer sufficient to meet the above demand.

In view of the above circumstances, the present invention has sought a new binder having excellent dispersibility of magnetic powder, imparting good electromagnetic conversion characteristics, and also showing good results in mechanical properties of the magnetic layer. By doing so, it is intended to overcome the above-mentioned conventional problems.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to achieve the above object, and as a result, (meth) acrylic acid alkyl ester-based polymer having a specific group at one end of a molecule, The dispersibility of the magnetic powder is improved when it is used in combination with various organic compounds having a lower molecular weight than this polymer and having a polar group at the end of the molecule,
The inventors have found that a magnetic recording medium having excellent electromagnetic conversion characteristics, good mechanical strength of the magnetic layer, and excellent durability can be obtained, and completed the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a non-magnetic support, wherein the binder has a (meth) acryl having a carboxyl group at the terminal of one molecule. The present invention relates to a magnetic recording medium comprising an acid alkyl ester-based polymer and an organic compound having a lower molecular weight than the above-mentioned polymer having a polar group at a terminal of a molecule.

[0009]

According to the present invention, a (meth) acrylic acid alkyl ester-based polymer having a carboxyl group at the end of a molecule has a carboxyl group at the end of the molecule attached to the surface of the magnetic powder. Adsorb,
This produces a steric repulsion effect between the adsorbing resins. Also,
Since the organic compound having a lower molecular weight than this acrylic resin has a stronger affinity with the magnetic powder surface than the acrylic resin and the size of the molecule is smaller, the gap of the acrylic resin adsorption layer is sewn to reach the surface of the magnetic powder. , Is fixed to the active sites on the surface of the magnetic powder by chemisorption.

Therefore, when the acrylic resin and the organic compound are used in combination, an adsorption layer having a higher binder component density than the adsorption layer of the acrylic resin alone is formed on the surface of the magnetic powder, The steric repulsion effect of the adsorption layer is much larger than that of the acrylic resin alone and compared with the conventional adsorption layer of the polar group-containing polyurethane resin, so that the dispersibility of the magnetic powder is remarkably improved. .

Further, as described above, since an adsorption layer having a very high density of the binder component is formed on the surface of the magnetic powder, polyisocyanate which is generally added to the magnetic paint for the purpose of improving the mechanical strength of the magnetic layer. -It is possible to prevent the crosslinking agent component such as grit from approaching the surface of the magnetic powder and reacting with the active sites on the surface to reduce the crosslinking efficiency of the binder component, and thus to have good mechanical properties and It also has excellent durability.

As described above, at least a part of the binder component of the magnetic powder is prepared by using an acrylic resin having a carboxyl group at the end of a molecule and an organic compound having a lower molecular weight than the above-mentioned polymer having a polar group at the end of the molecule. When used as a component, the dispersibility of the magnetic powder is sufficiently improved, and a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent durability can be obtained.

The above acrylic resin used in the present invention may be manufactured by any method. For example, a monomer mainly composed of (meth) acrylic acid alkyl ester is radically polymerized by a conventional method using a chain transfer agent having a carboxyl group in the molecule,
The so-called macro-monomer method and the same monomers as above are
It can be produced by a method such as radical polymerization by a conventional method using a polymerization initiator having a carboxyl group in the molecule such as 4,4′-azobis (4-cyanopentanoic acid).

In the case of the above macromonomer method, as the polymerization initiator, α.α'-azobisisobutyronitrile,
Benzoyl peroxide or the like can be used, and as the chain transfer agent containing a carboxyl group in the molecule, thiomalic acid, 3-mercaptopropionic acid, orthomercaptobenzoic acid or the like can be used.

The (meth) acrylic acid alkyl ester is
An alkyl ester of acrylic acid or methacrylic acid,
For example, methyl methacrylate, ethyl methacrylate
, Propyl methacrylate, butyl methacrylate,
Methacrylates such as hexyl methacrylate, lauryl methacrylate, stearyl methacrylate, and acrylates having an alkyl group similar to the above are mentioned, and one of them is used alone. These or two or more kinds can be mixed and used.

This (meth) acrylic acid alkyl ester may be used alone or, together with this (meth) acrylic acid alkyl ester, a monomer containing an active hydrogen group in the molecule, styrene or a derivative thereof, You may use together various monomers, such as acrylonitrile, methacrylonitrile, and vinyl acetate. Among these, when a monomer containing an active hydrogen group in the molecule is used, the active hydrogen group can be introduced into the molecule of the resulting acrylic resin, and by this introduction, sufficient reaction with a polyisocyanate cross-linking agent or the like can be achieved. Can be formed to form a magnetic layer having a three-dimensional network structure, so that particularly desirable results can be obtained for improving the durability of the magnetic layer.

Examples of the monomer having an active hydrogen group in the molecule include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate. There is a hydroxyl group-containing monomer such as G., and acrylamide and methacrylamide may also be used.

The acrylic resin obtained by such a method has a number average molecular weight (by vapor pressure permeation method) of 500 to 5
It is preferably in the range of 10,000. If the number average molecular weight is less than 500, the properties of the acrylic resin will not be exhibited, and if it exceeds 50,000, the degree of freedom of the acrylic resin will be reduced, and the dispersibility of the magnetic powder when the magnetic coating material is prepared will be reduced. .

Further, the number of carboxyl groups at the terminal of one molecule of the acrylic resin is preferably 1 to 3. Furthermore, when the above-mentioned active hydrogen group is introduced into the molecule of this acrylic resin, the amount of this active hydrogen group is 0.
It is preferably 2 to 5 mmol / g. If it is less than 0.2 mmol / g, it will be a strong 3 due to the reaction with the crosslinking agent.
A dimensional mesh structure cannot be formed, and improvement in durability cannot be expected.
Further, if it is more than 5 mmol / g, the viscosity when dissolved in an organic solvent usually used for magnetic paints becomes high,
It becomes difficult to use magnetic paint.

In the present invention, the organic compound used in combination with the above acrylic resin is a polar group such as a carboxyl group, an amino group, a phosphoric acid group or a sulfonic acid group, which is chemically adsorbed at the end of the molecule on the active site of the magnetic powder surface. , These salts,
Betaine, epoxy group, amide group, isocyanate group,
It has at least one polar group selected from the group consisting of triethoxysilyl group, trichlorosilyl group and hydroxyl group.

Further, this organic compound needs to have a lower molecular weight than the acrylic resin used in combination, and it is usually preferable that the organic compound has a molecular weight of half or less of that of the acrylic resin. When the molecular weight is higher than this, the molecule becomes larger,
It becomes difficult to chemically adsorb on the surface of the magnetic powder through the gap of the acrylic resin adsorption layer, and it becomes difficult to form an adsorption layer with a high binder component density on the surface of the magnetic powder, so a sufficient steric repulsion effect is obtained. Is not achieved and the dispersibility of the magnetic powder is reduced.

The number average molecular weight of the organic compound is preferably 100 to 20,000, more preferably 150 to 10,000. If the molecular weight is too small, the steric repulsion effect necessary for dispersion of the magnetic powder will be insufficient, and conversely, if it is too large, the degree of freedom of the polar group in the organic compound will decrease and adsorption on the magnetic powder surface will occur. It becomes difficult and causes a decrease in dispersibility.

As typical examples of such organic compounds, stearic acid, alkylmalonic acid, stearylamine, salts thereof, stearyl isocyanate, 1.2-
Polar group-containing aliphatic compounds such as epoxy octadecane,
Examples include coupling agents such as octadecyltriethoxysilane and octadecyltrichlorosilane, those containing the above compounds containing multiple bonds or active hydrogen in the molecular chain, and acrylic resins having a polar group at one end.

If desired, two or more of these organic compounds can be used. In this case, after the acrylic resin adsorption layer is formed on the surface of the magnetic powder, they are sequentially added, but organic compounds that do not chemically react with each other are mixed. You may add all at once.

The amount of such organic compound used is
It is usually 1-2 with respect to 100 parts by weight of the acrylic resin.
The amount is preferably 00 parts by weight, preferably 5 to 70 parts by weight. If the amount is too small, a sufficient steric repulsion effect cannot be obtained. On the contrary, if the amount is too large, the mechanical properties of the magnetic layer are deteriorated and durability is deteriorated.

In the present invention, the above-mentioned acrylic resin and organic compound can be used alone as a binder for magnetic powder, but they are usually used in a mixed system with another binder resin. Other binder resins include polyurethane resins, vinyl chloride-vinyl acetate copolymers, fibrin resins, polyvinyl butyral resins, polyester resins, polyacrylic resins, epoxy resins, phenol resins. Conventionally known binder resins such as resin and the like can be widely used, and polyisocyanate together with these resin components.
A crosslinking agent or the like is also used.

In these usage modes, the amounts of the acrylic resin and the organic compound used are 100% by weight of the magnetic powder in terms of the dispersibility of the magnetic powder and the durability of the magnetic layer. 0.1 to 35 parts by weight, particularly preferably 0.5 to 15 parts by weight.

To manufacture the magnetic recording medium of the present invention,
For example, first, an acrylic resin having a carboxyl group at the end of a molecule is dissolved in an organic solvent and mixed and dispersed with magnetic powder, and then an organic compound having a polar group at the end of the molecule is dissolved in an organic solvent or directly. Add to
Mix and disperse. Next, the remaining binder resin, other additives and the like are added together with the organic solvent, and further mixed and dispersed to prepare a magnetic coating material. Then, this magnetic coating material is applied onto a substrate such as polyester film by any means such as spraying or roll coating, and dried to form a magnetic layer having a thickness of usually about 0.1 to 20 μm. Good.

At this time, a back coat layer may be provided on the opposite surface, or a magnetic layer may be provided on both surfaces of the substrate. When a back coat layer is provided on the opposite surface, the above-mentioned acrylic resin having a carboxyl group at the end of the molecule and the organic compound having a polar group at the end of the molecule are preferably used as a binder for the back coat layer. It

As the magnetic powder, for example, γ-Fe ₂
O ₃ , Fe ₃ O ₄ , iron oxide in an intermediate oxidation state between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , CrO ₂ , Ba ferrite, etc. Oxide magnetic powder of Fe, Co, Fe-Co alloy, Fe-Co
Any magnetic powder conventionally used for magnetic recording media, such as metallic magnetic powders such as -Ni alloy, Fe-Ni alloy, Fe-Ni-Cr alloy, etc., and nitride-based magnetic powders such as iron nitride can be used. .

When these magnetic powders are composed of acicular particles, the average major axis diameter is about 0.2 to 1.0 μm, and the average axial ratio (average major axis diameter / average minor axis diameter) is 5 to 12. Something is preferable. Further, in the case of particles made of plate-like particles, those having an average plate diameter of about 0.07 to 3 μm are preferable.

As the organic solvent used for the magnetic paint, various organic solvents generally used for magnetic paints such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane and dimethylformamide are used alone. Or a mixture of two or more. Further, as the additive to be added to the magnetic paint, various commonly used additives such as a lubricant, an abrasive, an antistatic agent and a dispersant may be optionally used.

[0033]

As described above, according to the present invention, as a binder for magnetic powder, an acrylic resin having a carboxyl group at the end of a molecule and an organic compound having a polar group at the end of a molecule are used in combination. It is possible to provide a magnetic recording medium having excellent dispersibility of magnetic powder, excellent electromagnetic conversion characteristics, and good mechanical strength of the magnetic layer, and excellent durability.

[0034]

EXAMPLES Next, examples of the present invention will be described to explain more specifically. In the following, "parts" means "parts by weight". In addition, the acrylic resin A used in the examples
E is synthesized by the methods of Synthesis Examples 1 to 5 below.

Synthesis Example 1 Methyl methacrylate 50 parts α.α'-azobisisobutyronitrile 0.8 part Mercaptopropionic acid 3.2 parts Tetrahydrofuran 60 parts

The above composition was placed in a flask equipped with a condenser, and after thoroughly purging with nitrogen, the mixture was reacted at 60 ° C. for 3 hours while stirring. The reaction product obtained is then purified by reprecipitation in petroleum ether and water.
After drying under reduced pressure at 48 ° C. for 48 hours, an acrylic resin A having a carboxyl group at the end of a molecular piece was obtained. The acrylic resin A had a number average molecular weight of 3,000 as measured by the vapor pressure permeation method and a carboxyl group content of 0.3 mmol / g.

Synthesis Example 2 An acrylic resin B having a carboxyl group at one end of a molecule was obtained in the same manner as in Synthesis Example 1 except that the amount of mercaptopropionic acid used was changed to 1.6 parts. The acrylic resin B had a number average molecular weight of 6,000 and a carboxyl group content of 0.17 mmol / g as measured by the vapor pressure permeation method.

Synthesis Example 3 An acrylic resin C having two carboxyl groups at one end of a molecule was obtained in the same manner as in Synthesis Example 1, except that 2.3 parts of thiomalic acid was used instead of mercaptopropionic acid. The acrylic resin C had a number average molecular weight of 3,100 as measured by a vapor pressure permeation method, and a carboxyl group content of 0.
It was 65 mmol / g.

Synthesis Example 4 Methyl methacrylate 40 parts 2-Hydroxyethyl methacrylate 8.4 parts α.α'-azobisisobutyronitrile 0.8 parts Mercaptopropionic acid 1.6 parts Tetrahydrofuran 60 parts

Synthesis Example 1 except that the above composition was used
In the same manner as described above, an acrylic resin D having a carboxyl group at one end of the molecule was obtained. The acrylic resin D had a number average molecular weight of 6,000 by a vapor pressure permeation method, a carboxyl group content of 0.17 mmol / g, and a hydroxyl group content as an active hydrogen group of 1.2 mmol / g.

Synthesis Example 5 Synthesis Example 4 except that 2.3 parts of thiomalic acid was used instead of mercaptopropionic acid and 4.5 parts of acrylamide was used instead of 2-hydroxyethyl methacrylate.
In the same manner as described above, an acrylic resin E having two carboxyl groups at one end of the molecule was obtained. The acrylic resin E had a number average molecular weight of 3,100 as measured by a vapor pressure permeation method, a carboxyl group content of 0.65 mmol / g, and an amide group content as an active hydrogen group of 1.0 mmol / g. .

Example 1 100 parts of α-Fe magnetic powder (coercive force 1,500 oersted, saturation magnetization 120 emu / g), acrylic resin A4
Parts, 20 parts of cyclohexanone and 20 parts of toluene were added and mixed and dispersed in a ball mill for 12 hours. Then, 2 parts of stearylamine was added and mixed and dispersed in a ball mill for 8 hours.

Further, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by U.C.C.),
Polyurethane resin (M-5 manufactured by Nippon Polyurethane Industry Co., Ltd.
033) Add trifunctional low molecular weight isocyanate (Coronet L manufactured by Nippon Polyurethane Industry Co., Ltd.) and other coating components, and mix and disperse with a ball mill for 72 hours.
A magnetic paint having the following final composition was prepared.

Α-Fe magnetic powder 100 parts Acrylic resin A 4 parts Stearylamine 2 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts Polyurethane resin 8 parts Trifunctional low molecular weight isocyanate 2 parts Carbon black 3 parts α-Al ₂ O ₃ powder 3 parts myristic acid 2 parts n-butyl stearate 2.5 parts cyclohexanone 130 parts toluene 130 parts

The above magnetic coating material was applied onto a polyester film having a thickness of 20 μm so that the thickness after drying was 5 μm, and dried to form a magnetic layer, which was cut into 8 mm width after calendaring. Then, a magnetic tape was produced.

Example 2 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of acrylic resin B was used instead of acrylic resin A.

Example 3 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of acrylic resin C was used instead of acrylic resin A.

Example 4 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of acrylic resin D was used instead of acrylic resin A.

Example 5 A magnetic tape was produced in the same manner as in Example 1 except that the same amount of acrylic resin E was used instead of acrylic resin A.

Example 6 A magnetic tape was produced in the same manner as in Example 1 except that 1.5 parts of stearic acid was used instead of stearylamine.

Example 7 Instead of adding 2 parts of stearylamine and mixing and dispersing in a ball mill for 8 hours, 1 part of stearylamine was added and mixed and dispersed in a ball mill for 4 hours, and then 1 part of stearic acid was added. A magnetic tape was produced in the same manner as in Example 1 except that was added and mixed and dispersed in a ball mill for 4 hours.

Example 8 A magnetic tape was produced in the same manner as in Example 1 except that 2 parts of hexadecylmalonic acid was used instead of stearylamine.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that 4 parts of acrylic resin A and 2 parts of stearylamine were not used.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1 except that 2 parts of stearylamine was not used.

For each magnetic tape obtained in Examples 1 to 8 and Comparative Examples 1 and 2, the C / N ratio was determined by the following method.
The ratio, RF power and durability were measured. The results of these measurements are shown in Table 1 below.

<C / N ratio> Using a VTR of 8 mm system, a signal of 7 MHz was recorded on each magnetic tape, and the noise generated in the range of 7 ± 1 MHz when this signal was reproduced was measured, The ratio of the reproduced signal to this noise was measured using an ED-V900 type output level measuring instrument manufactured by Sony Corporation, and shown as a relative value with the magnetic tape of Comparative Example 1 as a reference (0 dB). .

<RF Output> Using a VTR for RF output measurement, after recording a signal of 7 MHz on each magnetic tape at a constant level, the output when reproduced was measured, and the magnetic tape of Comparative Example 1 was measured. Is shown as a relative value with reference to (0 dB).

<Durability> 20 ° C. for each magnetic tape
Under a condition of 40% RH and a condition of 40 ° C. and 60% RH, reproduction was carried out in a VTR still mode, and the time until the reproduction RF output level decreased to 1/2 of the initial output level was measured.

[0059]

[Table 1]

As is apparent from Table 1 above, Example 1
The magnetic tapes Nos. 8 to 8 have a higher C / N ratio and RF output and are more durable than the magnetic tapes of Comparative Examples 1 and 2, and from this fact, the magnetic recording media of the present invention are Indicates that the magnetic powder has good dispersibility, excellent electromagnetic conversion characteristics, and excellent durability.

Claims (4)

[Claims] 1. A magnetic recording medium provided with a magnetic layer containing a magnetic powder and a binder on a non-magnetic support, wherein the binder is a (meth) acrylic acid alkyl ester type having a carboxyl group at one end of the molecule. A magnetic recording medium comprising a polymer and an organic compound having a lower molecular weight than the polymer having a polar group at one end of the molecule. 2. The magnetic recording medium according to claim 1, wherein the number average molecular weight of the (meth) acrylic acid alkyl ester-based polymer having a carboxyl group at one terminal of the molecule is 500 to 50,000. 3. A polar group of an organic compound is a carboxyl group, amino group, phosphoric acid group, sulfonic acid group, salts thereof,
Betaine, epoxy group, amide group, isocyanate group,
The magnetic recording medium according to claim 1, which is at least one selected from a triethoxysilyl group, a trichlorosilyl group, and a hydroxyl group. 4. The magnetic recording medium according to claim 1, wherein the organic compound has a number average molecular weight of 100 to 20,000.