JPS628329A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability and surface characteristic and to considerably improve an electromagnetic conversion characteristic by using a vinyl chloride copolymer having a quaternary ammonium salt as a polar group in the molecule as a binder for a magnetic layer. CONSTITUTION:The magnetic layer contains the vinyl chloride copolymer having the quaternary ammonium salt in the molecule as the binder. The vinyl chloride copolymer is introduced with the polar group (quaternary ammonium salt) to the side chain of the vinyl chloride copolymer and is the compd. expressed by the formula, where X denotes a monomer copolymerizable with a vinyl chloride, Y denotes a monomer having a vinyl group copolymerizable with a vinyl chloride and the quaternary ammonium salt. i, j, k respectively denote the degrees of polymn.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly to a binder contained in a magnetic layer formed on a non-magnetic support. This is related to the improvement of.

(Summary of the Invention) The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support. A vinyl chloride-vinyl acetate copolymer having a quaternary ammonium salt as a polar group is used to improve the dispersibility of the magnetic powder and the surface properties of the magnetic layer, thereby improving the durability and magnetic properties of the resulting magnetic recording medium.

This is an attempt to improve electromagnetic conversion characteristics, etc.

[Conventional technology]

In recent years, magnetic recording media, especially magnetic recording media for VTRs (video tape recorders), have been required to have improved magnetic properties and electromagnetic conversion properties in order to obtain high playback output even when recording at short wavelengths. There is.

As a countermeasure, efforts have been made to make the magnetic powder particles finer and to increase the magnetic force, and there is a strong tendency to increase the packing density of the magnetic powder in the magnetic layer, the so-called backing density.

On the other hand, conventionally used binders for magnetic recording media include vinyl chloride-vinyl acetate copolymer, vinyl chloride-propionic acid copolymer, and vinyl chloride-vinyl acetate copolymer.
Examples include vinyl chloride-based binders such as vinyl alcohol copolymers, among which the hydroxyl groups of vinyl alcohol contribute to the dispersibility of magnetic powder, and the active hydrogen of the hydroxyl groups reacts with isocyanate compounds to form a crosslinked structure. Vinyl chloride-vinyl acetate-vinyl alcohol copolymer is widely used because it increases the mechanical strength of the coating film it forms.

However, due to the increase in specific surface area due to the finer particles of magnetic powder and the increase in cohesive force due to higher magnetic force, the above-mentioned binders are unable to provide satisfactory dispersibility and surface properties, and banking of magnetic powder is difficult. Increasing the density has also become difficult.

Therefore, the durability, magnetic properties, and electromagnetic conversion properties were also insufficient. Alternatively, methods such as using a surfactant as a dispersant have been considered, but in this case, since the surfactant is a low molecular weight, the presence of this surfactant in the magnetic layer causes the powder to become powdery. Problems have arisen in terms of mechanical strength and durability, such as falling off and blooming due to changes over time.

Under these circumstances, there is a need for a binder that can further improve these properties. Techniques have been proposed in which polymers into which polar groups such as metal salts, acidic sulfuric esters or alkali metal salts thereof, carboxylic acids or metal salts thereof are introduced are used as binders.

However, although the binders produced by these technologies show some effect in improving dispersibility compared to conventional binders that do not have polar groups introduced, The performance against powder was insufficient.

[Problem that the invention seeks to solve]

As described above, there is no known binder that exhibits sufficient dispersibility even for ultrafine magnetic powder, and therefore magnetic recording media using ultrafine magnetic powder must have the required durability and magnetic properties. , it was difficult to ensure electromagnetic conversion characteristics.

Therefore, the present invention was proposed in order to eliminate the above-mentioned drawbacks in the technical field, and it greatly improves the dispersibility of magnetic powder and the surface properties of the magnetic layer, and has excellent durability and magnetic properties. The purpose is to provide a magnetic recording medium with good characteristics.

[Means for solving problems]

The inventors of the present invention have conducted intensive research over a long period of time to achieve the above-mentioned objectives, and have found that a vinyl chloride copolymer having a quaternary ammonium salt in its side chain exhibits high affinity for magnetic powder. They discovered this and completed the present invention, which provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support. It is characterized in that it contains a vinyl chloride copolymer having a quaternary ammonium salt as a binder.

In the present invention, the vinyl chloride copolymer contained in the binder is a vinyl chloride copolymer with a polar group (quaternary ammonium salt) introduced into the side chain, and has the general formula % formula %). (In the formula, X represents a monomer having a vinyl group copolymerizable with vinyl chloride, and Y represents a monomer having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt. (each represents the degree of polymerization). In addition, in the above general formula,
For convenience, each component of the compound is described as being arranged in a regular order, but in addition to the case shown in the general formula above,
It goes without saying that each component may be regularly and repeatedly arranged in a fixed proportion, or may be arranged randomly.

The monomer Y having a vinyl group and a quaternary ammonium salt that can be copolymerized with vinyl chloride is synthesized, for example, by the following method.

Cl -CHzCHz-C1+ KOH-1→C(1
-CHzCHt-OHCA -CHzCHz-OR+
N(R)s0H-CH2CH2-N"-R・C1-C
HlCH-COOH+ 0H-CHzCHt-N”
-R・CZ- (However, in the formula, R represents a hydrocarbon group such as an alkyl group.) Specifically, i) CHz-CHCOOCHgCH(OH)CH
tN"(CHs)s・C1-1i) CHz=CH
COOCH o C) I! N” (C, H5)!・CAl
-1ii) CHt-CHCOOCHzCHzCH
zCHtN” (CTo) s・CX-1V) CH
z−CHCOOCHtCHxCONH(CHz)+N”
(CLL・CZ-, etc. are mentioned.

In addition, the following monomers can also be used.

vi) CIkl=CHN"(CHs)3 ・Br-In addition to the above-mentioned copolymerizable monomers, from the viewpoint of improving solubility in solvents, crosslinking with isocyanate, and improving coating film strength,
At least one member selected from vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, vinylidene chloride, vinyl propionate, etc. can be copolymerized with vinyl chloride. It is also possible to copolymerize as a monomer X having a vinyl group.

Here, the degree of polymerization (t+j+
k) is preferably within the range of 100≦(i+j+k)≦1000. If this value is less than 100, the durability of the resulting coating film will deteriorate, and if it exceeds 1000,
The solubility in solvents deteriorates, making it difficult to form into paints.

Further, the proportion of the vinyl chloride component contained in the vinyl chloride copolymer is preferably 50 to 95 mol%. If the vinyl chloride component is too large or too small, durability will deteriorate.

The proportion of the monomer Y having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt in the vinyl chloride copolymer is preferably in the range of 0.1 to 20 mol%. If this proportion is less than 0.1 mol%, the dispersion effect on the magnetic powder will be insufficient, and if it exceeds 20 mol%, the moisture resistance of the resulting coating will deteriorate.

Furthermore, in order to improve the physical properties of the coating film, the vinyl chloride copolymer is copolymerized with a monomer X having a vinyl group that can be copolymerized with the vinyl chloride in a proportion of about 0 to 50 mol%. .

The vinyl chloride copolymer containing the above-mentioned quaternary ammonium salt may be used in combination with other binders6. Such binders include those conventionally used as binders for magnetic recording media. can be used, including vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, chloride Vinyl-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin, Phenoxy 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 polyurethane resin, urea resin, melamine resin, alkyd resin, urea - Formaldehyde resins or mixtures thereof. Among these, polyurethane resins, polyester resins, acrylonitrile butadiene copolymers, etc., which are said to impart flexibility, are preferred. Moreover, if a trifunctional isocyanate compound, a reaction product of 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate, etc. are used in combination as a crosslinking agent, durability etc. can be further improved. In any case, the polar group equivalent (molecular weight per polar group) of the quaternary ammonium salt, which is a polar group in these binders, is preferably within the range of 1,000 to 100,000. If this polar group equivalent exceeds 100,000, no effect can be expected, and if it is less than 1,000, the effect will not change much, but problems will arise in terms of moisture resistance.

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

Here, the material for the non-magnetic support may be any material that is normally used in this type of magnetic recording medium, such as polyesters such as polyethylene terephthalate, polyolefins such as polyethylene, polypropylene, etc. cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride 2 polyvinylidene chloride, plastics such as polycarbonate, polyimide, polyamide, and polyamideimide, paper, metals such as aluminum, copper, etc. , light alloys such as aluminum alloys and titanium alloys, ceramic fuchs, and single crystal silicon. Examples of the forms of this non-magnetic support include film and tape.

It may be a sheet, disk, card, drum, etc.

Moreover, any ordinary ferromagnetic powder can be used as the ferromagnetic powder used in the magnetic layer. Therefore, ferromagnetic powders that can be used include ferromagnetic iron oxide particles,
Examples include ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, iron nitride, and the like.

The above-mentioned ferromagnetic iron oxide particles are those whose X value is in the range of 1.33≦X≦1.50 when expressed by the general formula FeOx, that is, magnetite (γ-Fe, O,).

X=1.50), magnetite (F si O,, X-
1-33) and their solid solutions (FeOx, 1.33<
Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force.
There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide includes CRO, or Ru, Sn, and To for the purpose of improving coercive force.
, Sb, Fe, Ti, V, Mn, etc. can be used.

Examples of the ferromagnetic alloy powder include Fe, Co, and Ni.

Fe-Co, Fe-Ni, Fe-Co-Ni, Go-N
i, Fe-Co-B, Fe-Co-Cr-B, Mn-
Bt, Mn-Af, Fe-Co-V, etc. can be used, and Al, Si can be added to these for the purpose of improving various properties.
, Ti, Cr, Mn, Cu, Zn, and other metal components may be added.

In addition to the binder and ferromagnetic powder, the magnetic layer also contains additives such as a dispersant, a lubricant, an abrasive, an antistatic agent,
Rust inhibitors and the like may also be added.

The constituent materials of the magnetic layer described above are prepared as a magnetic paint by dissolving it in an organic solvent and coated on a non-magnetic support.The solvent for the magnetic paint may be acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. Ketones, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, etc.
Aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, methylene chloride and ethylene chloride.

R-tetrachloride, chloroform, ethylene chlorohydrin,
Examples include chlorinated hydrocarbons such as dichlorobenzene.

[Effect]

As mentioned above, by using a vinyl chloride copolymer containing a quaternary ammonium salt in the molecule as a binder, the affinity for magnetic powder is greatly improved, and ultrafine magnetic powder and magnetized Even large amounts of magnetic powder are well dispersed.

(Nitahaku) [Examples] Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

Resin synthesis example Select vinyl acetate as the monomer X, copolymerize it with vinyl chloride and a monomer Y having a vinyl group copolymerizable with vinyl chloride and a quaternary ammonium salt, and determine the ratio of these monomers and the type of monomer Y. A binder having a degree of polymerization of 400 was synthesized by changing the formula as shown in Table 1. In this Table 1, monomer a is CHZMCHCOOCHCH(OH)CH! N”(C
Hs) s・CX-, monomer b is CHg-(JICOOCHzGHzN' (CtHs)
3.CZ-, and the monomer d represents CHg=CHN"(CHz)s.Br-, respectively.

Table 1: Co adhesion 'r Fe! us 100 parts by weight (specific surface area 40 rd/g) Binder 1 14 parts by weight Polyurethane resin (N-2304) 6 parts by weight Dimethyl silicone oil 1 part by weight Lecithin (dispersant) 1 part by weight CrgOt
(Abrasive) 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 was mixed in a ball mill for 48 hours, filtered through a 3 μm filter, and then 2.5 parts by weight of a curing agent (Desmodur L, manufactured by Bayer AG) was added.
parts by weight, mixed for an additional 30 minutes, and added 14μ
The film was coated on a polyethylene terephthalate film with a thickness of 6 μm after drying, and then subjected to magnetic field orientation treatment, dried and rolled up. A sample tape was prepared by cutting the tape into pieces.

Example 2 A sample tape was prepared in the same manner as in Example 1 except that Binder 2 was used instead of Binder 1.

Example 3 A sample tape was prepared in the same manner as in Example 1 except that Binder 3 was used instead of Binder 1.

Example 4 A sample tape was prepared in the same manner as in Example 1 except that Binder 4 was used instead of Binder 1.

Example 5 A sample tape was prepared in the same manner as in Example 1 except that Binder 5 was used instead of Binder 1.

Example 6 A sample tape was prepared in the same manner as in Example 1 except that Binder 6 was used instead of Binder 1.

Comparative Example 1゜A sample tape was prepared in the same manner as in Example 1 except that a vinyl chloride-vinyl acetate copolymer (trade name: VAGH, U, C, C, manufactured by Co., Ltd.) was used instead of Binder 1. did.

Comparative Example 2 A sample tape was prepared in the same manner as in Example 1, except that a vinyl chloride-vinyl acetate copolymer (trade name: VMCH, U, C, C, manufactured by Co., Ltd.) was used instead of Binder 1. .

Surface gloss, powder removal, and still characteristics were measured for each sample tape obtained.

The above surface gloss was measured using a gloss meter (GLO3S METE).
R) under the conditions of an incident angle of 75'' and a reflection angle of 75°.In addition, the amount of powder falling on the head drum 9 guide etc. was visually observed after running the shuttle 100 times for 60 minutes. The still characteristics were evaluated using the deduction method (-5 to 0).
A 4.2MH1 video signal was recorded on a sample tape, and the time until the playback output attenuated to 50% was taken as the time. The results are shown in Table 2.

Table 2 From this table, it can be seen that each sample tape according to the present invention not only has excellent surface gloss and powder removal, but also has significantly improved still characteristics. [Effects of the invention] From the above explanation, As is also clear, in the present invention,
Since the binder for the magnetic layer is a vinyl chloride copolymer that has a quaternary ammonium salt as a polar group in the molecule,
It shows a high affinity for magnetic powder, and even if it is an ultrafine magnetic powder or a magnetic powder with a large amount of magnetization, it will have good dispersibility. Therefore, the durability and surface properties of the obtained magnetic recording medium are improved, and the electromagnetic conversion characteristics are also extremely excellent.

Claims (1)

[Scope of Claims] A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the magnetic layer has a quaternary ammonium salt in its molecules. A magnetic recording medium characterized by containing a vinyl copolymer as a binder.