JPH0738252B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, and more specifically, a binder contained in a magnetic layer formed on a non-magnetic support. Related to the improvement of.

[Outline of Invention]

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the magnetic layer comprises a phenoxy resin having a quaternary ammonium salt in its side chain. By including it as a binder, the dispersibility of the magnetic powder and the surface property of the magnetic layer are improved, and the durability, magnetic characteristics, electromagnetic conversion characteristics, etc. of the obtained magnetic recording medium are improved.

[Conventional technology]

In recent years, in magnetic recording media, especially VTR (video tape recorder) magnetic recording media, improvement in magnetic characteristics and electromagnetic conversion characteristics has been demanded in order to obtain high reproduction output even when recording at short wavelength. There is. As a measure to this end, the magnetic powder is made finer and the magnetic force is increased, and the tendency is to increase the packing density of the magnetic powder in the magnetic layer, so-called packing density.

On the other hand, as a binder for a magnetic recording medium that has been conventionally used, vinyl chloride-vinyl acetate copolymer, vinyl chloride-propionic acid copolymer, vinyl chloride-vinyl acetate-
Vinyl chloride-based binders such as vinyl alcohol copolymers can be mentioned. Among them, the hydroxyl group of vinyl alcohol contributes to the dispersibility of the magnetic powder, and active hydrogen of the hydroxyl group reacts with an isocyanate compound to form a crosslinked structure. Vinyl chloride-vinyl acetate-vinyl alcohol copolymers are widely used because of the increased mechanical strength of the coating film formed.

[Problems to be solved by the invention]

However, with the increase in specific surface area due to atomization of the magnetic powder as described above and the increase in cohesive force due to high magnetizing force, satisfactory dispersibility and surface property cannot be obtained with the above-mentioned binder, and the packing of the magnetic powder Increasing the density is also difficult. Therefore, durability, magnetic characteristics,
The electromagnetic conversion characteristics were also insufficient.

Further, for example, a method of using a surfactant as a dispersant has been considered, but in this case, since the surfactant is a low molecule, the presence of this surfactant in the magnetic layer causes There is a problem with mechanical strength and durability such as blooming due to falling and aging.

Therefore, the present invention has been proposed in order to eliminate the above-mentioned drawbacks of the technical field, and provides a binder having excellent dispersibility of magnetic powder and good coating strength, thereby improving durability. It is an object of the present invention to provide a magnetic recording medium having excellent magnetic characteristics and electromagnetic conversion characteristics.

[Means for solving problems]

The inventors of the present invention found that the phenoxy resin having a quaternary ammonium salt in the side chain exhibits a high affinity for the magnetic powder as a result of earnest research over a long period of time without achieving the above object. In a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a non-magnetic support, the magnetic layer has a quaternary side chain. It is characterized by containing a phenoxy resin having an ammonium salt as a binder.

The phenoxy resin used in the present invention has excellent coating strength and is produced from, for example, bisphenol A and epichlorohydrin. Its basic structure is represented by the following structural formula (I).

(However, in the formula, n represents an integer of 20 to 200.) In order to introduce a quaternary ammonium salt as a hydrophilic polar group into the phenoxy resin, a hydroxyl group of a side chain of the phenoxy resin is used, This may be modified with a compound having a group capable of reacting with active hydrogen and a quaternary ammonium salt in the molecule.

The compound having a group capable of reacting with active hydrogen and a quaternary ammonium salt in the molecule is represented by the following formula (However, in any of the above polar groups, R has 1 carbon atom.
To 4 alkyl groups, X represents Cl, Br, I and m represents 2 or 3, respectively. ) And the like.

These compounds are synthesized as follows.

The following may be mentioned as specific examples of the compound.

When a compound having a group capable of reacting with active hydrogen and a quaternary ammonium salt in the molecule is reacted with a phenoxy resin, the --NCO group remaining in the former reacts with the --OH group in the phenoxy resin. A phenoxy resin having a quaternary ammonium salt, which is a hydrophilic polar group, is obtained.

If the reaction formula is specifically shown, it is as follows.

In the phenoxy resin in which the hydrophilic polar group synthesized as described above is introduced into the side chain, the introduced amount of the polar group is 0.01
It is preferably about 0.35 mmol / g. Introduction amount 0.01 mmol
If it is less than / g, the dispersibility of the magnetic powder will be poor, and if it is more than 0.35 mmol / g, the solubility in the solvent will be poor and the moisture resistance of the coating film will be poor.

The molecular weight of the phenoxy resin is preferably in the range of 5,000 to 100,000 when preparing the magnetic coating material.
If the molecular weight is 5000 or less, the durability is poor, and if it is 100000 or more, the solubility in a solvent is deteriorated.

The phenoxy resin having the quaternary ammonium salt introduced therein may be used as a mixture with another binder. As such a binder, those conventionally used as a binder for a magnetic recording medium can be used, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride. -Vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester- Vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting Examples thereof include polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin, and mixtures thereof. Among them, polyurethane resin, polyester resin, acrylonitrile butadiene copolymer, etc., which are said to impart flexibility, are preferable.

In the magnetic recording medium of the present invention, the magnetic layer is formed, for example, by coating the surface of the non-magnetic support with a magnetic paint prepared by dispersing ferromagnetic powder in the above binder and dissolving it in an organic solvent.

Here, as the material of the non-magnetic support, any material can be used as long as it is usually used for this kind of magnetic recording medium, for example, polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene. , Cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, plastics such as polycarbonate, polyimide, polyamide and polyamideimide,
Examples thereof include paper, metals such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon. The form of this non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like.

As the ferromagnetic powder used in the magnetic layer, any ordinary powder can be used. Therefore, examples of the ferromagnetic powder that can be used include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, and iron nitride.

As the above-mentioned ferromagnetic iron oxide particles, when represented by the general formula FeOx, those having an X value in the range of 1.33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1.50), magnetite (Fe ₃
O ₄ , X = 1.33) and their solid solutions (FeOx, 1.33 <X <1.5
0). Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing iron oxide is roughly classified into two types: a doped type and an adhered type.

As the above-mentioned ferromagnetic chromium dioxide, CrO or those obtained by adding at least one kind of Ru, Sn, Te, Sb, Fe, Ti, V, Mn or the like to improve coercive force can be used.

As the ferromagnetic alloy powder, Fe, Co, Ni, Fe-Co, Fe-Ni, Fe
-Co-Ni, Co-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn
-Al, Fe-Co-V and the like can be used, and metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added to these for the purpose of improving various characteristics.

Further, in the magnetic layer, in addition to the binder and the ferromagnetic powder, an additive such as a dispersant, a lubricant, an abrasive, an antistatic agent,
A rust preventive agent or the like may be added.

The above-mentioned constituent materials of the magnetic layer are dissolved in an organic solvent to prepare a magnetic coating material, which is coated on a non-magnetic support, and the magnetic coating material solvent is acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, or the like. Ketone type, ester type such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate, glycol ether type such as glycol dimethyl ether, glycol monoethyl ether and dioxane,
Aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene. Can be mentioned.

[Action]

As described above, by using a phenoxy resin containing a quaternary ammonium salt as a polar group in the molecule as a binder, the affinity for the magnetic powder is significantly improved, and the amount of magnetization of the ultrafine magnetic powder is increased. Even a magnetic powder having a large particle size is well dispersed.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

First, a phenoxy resin containing a quaternary ammonium salt was synthesized.

Synthesis Example 1 A phenoxy resin having an average degree of polymerization of 50 was used. Polymer A was modified with a compound represented by the formula (1) at a rate of 0.03 mmol / g.

Synthesis Example 2 A phenoxy resin having an average degree of polymerization of 50 was used. Denatured at a rate of 0.07mmol / g by the compound shown in,
This was designated as Polymer B.

Synthesis Example 3 A phenoxy resin having an average degree of polymerization of 50 was used. Denatured at a rate of 0.14 mmol / g with the compound shown by
It was designated as Polymer C.

Synthesis Example 4 A phenoxy resin having an average degree of polymerization of 50 was used. Denatured at a rate of 0.07mmol / g by the compound shown in,
This was designated as polymer D.

Synthesis Example 5 A phenoxy resin having an average degree of polymerization of 60 was used. Denatured at a rate of 0.07mmol / g by the compound shown in,
It was designated as polymer E.

Next, a magnetic recording medium was produced using the polymer (phenoxy resin having a quaternary ammonium salt) obtained in the above synthesis example.

Example 1 100 parts by weight of ferromagnetic powder (specific surface area 35 m ² / g, Co-γ iron oxide) Polymer A 12 parts by weight Polyester polyurethane resin 8 parts by weight (Polyurethane Industry Co., Ltd., N-2304) Lubricant (dimethyl silicone oil) ) 1 part by weight Lubricant (hexyl laurate) 1 part by weight Dispersant (lecithin) 1 part by weight Abrasive (Cr ₂ O ₃ ) 3 parts by weight Antistatic agent (carbon) 2 parts by weight Methyl ethyl ketone 100 parts by weight Methyl isobutyl ketone 50 Parts by weight Toluene 50 parts by weight The above composition is mixed in a ball mill for 48 hours, filtered through a filter, a curing agent is added, and the mixture is further mixed for 30 minutes, which is then dried on a 16 μm-thick polyethylene terephthalate film. It was applied so as to have a thickness of 6 μm. Next, after performing a magnetic field orientation treatment, it was dried and wound. This was calendered and then cut into a 1/2 inch width to obtain a sample tape.

Example 2 A sample tape was produced in the same manner as in Example 1 except that the polymer B was used instead of the polymer A in Example 1.

Example 3 A sample tape was produced in the same manner as in Example 1 except that Polymer C was used instead of Polymer A in Example 1.

Example 4 A sample tape was produced in the same manner as in Example 1 except that Polymer D was used instead of Polymer A in Example 1.

Example 5 A sample tape was produced in the same manner as in Example 1 except that the polymer E was used instead of the polymer A in Example 1.

Comparative Example 1 A sample tape was prepared by the same method as in Example 1 except that the polymer A contained in the coating solution in Example 1 was an unmodified phenoxy resin having an average degree of polymerization of 50 without modifying the polar group. Was produced.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1 except that the polymer A contained in the coating solution in Example 1 was an unmodified phenoxy resin having an average degree of polymerization of 60 and the polar group was not modified. Was produced.

With respect to each of the obtained sample tapes, surface gloss, powder falling, and still characteristics were measured.

The surface gloss was measured using a gloss meter (GLOSS METER) under the conditions of an incident angle of 75 ° and a reflection angle of 75 °. Also,
The powder drop is the head drum after 100 runs of the shuttle for 60 minutes,
Visually observe the amount of powder falling on the guide, etc., and use the deduction method (-5
.About.0). Still characteristics are 4.
The time for recording a 2MHz video signal and for the playback output to decay to 50% was used. The results are shown in the table below.

From this table, it can be seen that the sample tapes according to the present invention not only have excellent surface gloss and powder falling, but also have significantly improved still characteristics.

〔The invention's effect〕

As is clear from the above description, in the present invention,
A phenoxy resin containing a quaternary ammonium salt as a polar group in the molecule is used as a binder for the magnetic layer, so that it has a high affinity for magnetic powder, even if it is made into ultrafine magnetic powder or magnetized with a large amount of magnetization. Even the powder has good dispersibility. Therefore, the durability and surface property of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly containing a ferromagnetic powder and a binder, wherein the magnetic layer is a phenoxy resin represented by the following structural formula (I). A magnetic recording medium containing as a binder a phenoxy resin having a quaternary ammonium salt in its side chain, which is synthesized by the reaction of a compound represented by the following structural formula (II) with: (However, in the formula, n represents an integer of 20 to 200.) (However, R in the formula is an alkyl group having 1 to 4 carbon atoms, and X is
Represents Cl, Br, or l, respectively, and m is 2 or 3
Is. )