JPS63271710A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility and long-period durability of fine ferromagnetic powder by forming a magnetic layer dispersed with the ferromagnetic powder in a binder resin essentially consisting of a vinyl chloride copolymer which is modified with amine and contains a sulfonic acid group on a base. CONSTITUTION:The magnetic layer dispersed with the fine ferromagnetic powder into the binder resin essentially consisting of the vinyl chloride copolymer which is modified with the amine and contains the sulfonic acid group is formed on the base. The vinyl chloride copolymer which is the essential component of the binder resin particularly preferably has 60-95wt.% vinyl chloride unit, 0.05-5wt.% as bond nitrogen, 0.05-1.0wt.% as sulfonic acid group and some ratio of the other vinyl units to be added at need and has 200-800 average degree of polymn. Since the dispersibility of the ferromagnetic powder is good, the magnetic layer having a high residual magnetic flux density and squareness ratio is obtd.; in addition, gloss is good, powder dislodgment is decreased and the durability is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a special copolymer mainly composed of vinyl chloride, which has excellent performance as a binder for magnetic recording media, especially ferromagnetic fine powder. This invention relates to an improved magnetic recording medium.

[Prior art and its problems] Magnetic recording media such as magnetic tape generally have magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film.
It is made by providing a coating film consisting of. Magnetic powders include γ-Fe20s%Fe504, those adsorbed or doped with cobalt ions, CrO□, Fe%Go, Fe
Acicular fine particle materials containing -Co or Ni in some cases are used, but in recent years, as the performance of video tapes and audio tapes has improved, high density and high playback output in short wavelength recording have been required. There is. In order to cope with these trends, magnetic powders have been made into finer particles than ever before, and because they have a very large magnetic moment, the particles tend to agglomerate with each other, resulting in a uniform distribution of particles into the binder resin. Diversification is becoming more difficult than ever. In order to solve this technical problem, a wide range of studies have been conducted from the viewpoint of improving the affinity of the binder resin for magnetic powder. For example, binder resins with carboxyl groups, hydroxyl groups, etc. introduced into their molecular structures have been put into practical use, but the dispersibility of ferromagnetic powders in these resins is still insufficient, and as a result, residual magnetic flux density, squareness ratio, etc. However, it has the disadvantage of being unsatisfactory, and is prone to powder falling off, resulting in poor durability.

[Means for Solving the Problems] The present inventor has solved these conventional drawbacks, developed a binder resin with further improved dispersibility, and has conducted intensive research to obtain a high-performance magnetic recording medium. , arrived at the present invention.

That is, the present invention is formed by forming on a support a magnetic layer in which fine ferromagnetic powder is dispersed in a binder resin mainly composed of a vinyl chloride copolymer that is amine-modified and has a sulfonic acid group. It relates to magnetic recording media.

The vinyl chloride copolymer used in the magnetic layer of the present invention has excellent dispersibility and high filling properties for ferromagnetic powder, and has sufficient compatibility with appropriately used polyurethane resins, etc. When used as an agent resin, a high-performance magnetic recording medium with improved long-term durability can be obtained.

The present invention will be explained in detail below.

In particular, the vinyl chloride copolymer which is the main component of the binder resin used in the present invention has (a) 60 to 95 vinyl chloride units.
% by weight, (b) O, OS ~ 5% by weight as bound nitrogen, (
c) It is desirable to have an average degree of polymerization of 200 to 800, containing 0.05 to 1.0% by weight of sulfonic acid groups and a slight amount of other vinyl units added as necessary. If the amount of vinyl chloride units as component (a) is too small, the physical strength will decrease, while if it is too large, the solubility will decrease, which is disadvantageous in use. The amine-modified vinyl unit forming the basis of component (b) can be introduced by treating the vinyl chloride copolymer with various amine compounds described below.

The mechanism by which nitrogen is introduced by amine-modifying a vinyl chloride copolymer is unknown, but even if the amine-modified copolymer of the present invention is repeatedly purified by dissolving it in an organic solvent and reprecipitating, it cannot be purified by the Kel-Musin method. Nitrogen is quantified, and the bonding of nitrogen is also confirmed by nuclear magnetic resonance.

If the amount of bonded nitrogen is too small, disadvantages such as a decrease in dispersibility, a decrease in the smoothness of the coating film, and a decrease in reactivity with the isocyanate group-containing urethane prepolymer will occur. If the amount is too large, the dispersibility and smoothness will deteriorate, and the solubility will also decrease, making it impossible to use it as a binder resin.

Amine compounds used for this include aliphatic amines, alicyclic amines, aromatic amines, alkanolamines,
Includes primary, secondary or tertiary amines such as alkoxyalkylamines, specifically methylamine,
Ethylamine, propylamine, butylamine, cyclohexylamine, ethanolamine, naphthylamine,
Aniline, o-toluidine, diethylamine, dioctylamine, diisobutylamine, jetanolamine,
Diaminopropane, hexamethylene diamine, methylethanolamine, dimethylethanolamine, dibutylethanolamine, methyljetanolamine, 2-methoxyethylamine, di-2-methoxyethylamine,
N-methylaniline, trimethylamine, triethylamine, triisobutylamine, tridecylamine, N-
Methyldiphenylamine, hexamethylenetetramine,
Examples include triethanolamine, tributylamine, dimethylpropylamine, pyridine, α-picoline, β-picoline, γ-picoline, 2,4-lutidine, quinoline, morpholine, sodium taurate, potassium sulfanilate, naphthylamine sulfonic acid, etc. Ru.

Furthermore, even if an amine compound is added directly to a magnetic paint consisting of a ferromagnetic powder and a conventional binder resin and kneaded to create a magnetic coating film without reacting as in the present invention, the dispersion of the magnetic powder and the Although there is some effect on smoothing, the dispersibility of the magnetic powder in the paint decreases over time, making it impossible to achieve the desired effect.

(c) The sulfonic acid group of the component improves the dispersibility of the magnetic powder,
In particular, it is used to improve the dispersibility of fine particles of magnetic powder and metal powder, and examples of monomers corresponding to this (c) unit include the following.

CH2-C8503M, CHz-CI-CHzSO
sM, CH2=CH-CaH4S03M.

CH3 0? H3 0h-CH=CQO-(:zH4sOsM.

C1b-CH-CH20CHzCHCHzSOsM (where M represents a hydrogen atom or an alkali metal, and R represents an alkyl group).

The sulfonic acid group in the copolymer replaces the aforementioned 505M with 5O3H.
It is desirable that the content is 0.05 to 1.0% by weight, and if it is too little or too much, the dispersibility will deteriorate.

Note that there is no problem even if the above-mentioned amine-modified vinyl unit contains a sulfonic acid group. In this case, sulfonic acid groups are also introduced at the same time by amine modification.

Other vinyl units are used to improve the solubility and flexibility of the copolymer, or to facilitate the introduction of amine or sulfonic acid groups, and the corresponding monomer is vinyl acetate. , vinyl propionate, vinyl versatate (manufactured by Shell Chemical), vinyl stearate, vinyl benzoate, methyl (meth)acrylate (means methyl methacrylate and methyl acrylate; the same applies hereinafter), (meth)acrylic acid Ethyl, propyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylic@2-ethylhexyl, allyl glycidyl ether, glycidyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, ethyl Examples include vinyl ether, isobutyl vinyl ether, diethyl maleate, diethyl fumarate, dibutyl maleate, and dibutyl fumarate.

These vinyl units may be used alone or in combination of two or more thereof. Furthermore, a copolymer containing a vinyl ester may be saponified by a conventional method to convert a portion of the vinyl ester into vinyl alcohol.

This copolymer can be produced using general suspension polymerization method, emulsion polymerization method,
It can be produced by a solution polymerization method, a bulk polymerization method, or the like.

When using the above copolymer as a binder resin, other resins may be used in the same amount as necessary, and examples of resins that can be used in combination include polyurethane resins, nitrocellulose, epoxy resins, Polyamide resin, phenolic resin, acrylic ester, methacrylic ester, styrene, acrylonitrile, butadiene, ethylene, propylene, vinylidene chloride, acrylamide,
Examples include various polymers such as vinyl ethers and copolymers. Among these, polyurethane resins and nitrocellulose are particularly preferred.

In addition, it is desirable to use a polyisocyanate-based curing agent, such as bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, hexane diisocyanate, coronate (trade name manufactured by Nippon Polyurethane Industries), and dismodule. Examples include trifunctional isocyanates such as L (trade name, manufactured by Bayer AG), and urethane prepolymers containing isocyanate groups at both ends. The amount of these curing agents used should be 40 parts by weight or less per 100 parts by weight of the binder resin.

The ferromagnetic powder used in the present invention includes γ-”203
, Fe504 and these adsorbed or doped with cobalt ions, CrO2, etc., and furthermore, Fe%Co%Fe-Go or optionally N1 etc. are added to the acicular fine particle material, and various other conventionally known magnetic powders are used. The mixing ratio of the 0 ferromagnetic fine powder and the binder resin is 8 to 8 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic fine powder.
The amount is preferably 30 parts by weight.

In order to uniformly disperse the ferromagnetic powder and the binder resin, it is necessary to add commonly used lubricants, abrasives, antistatic agents, dispersion aids, rust preventives, etc., and to use a coating medium. Various other organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and toluene may be used as in the past, and there are no particular restrictions on these points.

Supports include synthetic resins such as polyester, polyolefin, cellulose acetate, and polycarbonate;
Other magnetic metals and ceramics are used, and they are used in the form of films, tapes, sheets, plates, etc.

The coating means for forming the magnetic layer on the support may be any conventionally known method, and by appropriately applying smoothing treatment such as calendaring treatment, the high-performance magnetic recording medium that is the object of the present invention can be obtained. is obtained.

[Example] Next, specific aspects of the present invention will be explained by giving examples and comparative examples.

Example 1 (Synthesis of Polymer 1) 40 methanol was added to an autoclave equipped with a stirring device.
0g of vinyl chloride, 80g of vinyl acetate, 36g of vinyl acetate, 4g of sodium vinylsulfonate, 2g of di(2ethylhexyl)peroxydicarbonate, and 2g of partially saponified polyvinyl alcohol, and the reaction was started by raising the temperature to 50°C while stirring under a nitrogen gas atmosphere. Furthermore, vinyl chloride 8
0 g was continuously injected over a period of 8 hours to cause a copolymerization reaction.

Autoclave internal pressure is 0.5kg/cm2 after 12 hours.
Since the residual pressure is removed and cooled, the copolymer slurry is taken out, filtered, and mixed with 1000 g of methanol three times.
After washing twice with 000 g of deionized water and filter drying, 150 g of copolymer powder was obtained, which contained 84.3% by weight of vinyl chloride, 14.5% by weight of vinyl acetate, and vinyl sulfonic acid. Average degree of polymerization 3, consisting of 1.2% by weight of soda
00 copolymer. 100 g of this copolymer, 200 g of methanol, and 5 g of dimethylethanolamine were added to a reactor equipped with a cooling tube, and the mixture was reacted at 40°C for 6 hours, washed three times with 1000 g of methanol, and further washed with i.
It was washed twice with OOOG deionized water, filtered and dried to obtain 93 g of modified copolymer powder.

This product contains 84.5% by weight of vinyl chloride and 14% by weight of vinyl acetate.
．． 1% by weight of O, 1.1% by weight of sodium vinyl sulfonate, i.e. 0.7% by weight in terms of sulfonic acid group, and 0.0% by weight of bound nitrogen.
It was a modified copolymer with an average degree of polymerization of 300 and 4% by weight.

Example 2 (Synthesis of Polymer 2) Into a reactor equipped with a cooling tube, 100 g of the copolymer obtained as the intermediate product of Synthesis Example 1, 200 g of methanol, 3 g of caustic soda, and 6 g of triethylamine were charged, and the mixture was heated with stirring for 40 g. The temperature was raised to ℃, reacted for 5 hours, and cooled.
6 g of acetic acid was added to neutralize unreacted caustic soda. This was washed four times with 200 g of methanol and twice with 200 g of deionized water, filtered and dried to obtain 86 g of a modified copolymer powder (Polymer 2), which contained 91. 0% by weight, vinyl acetate 0.6% by weight, vinyl alcohol 6.7% by weight, sodium vinyl sulfonate 1, l! % by weight, i.e. 0.7% by weight calculated as sulfonic acid group
, a bound nitrogen content of 0.08% by weight, and an average degree of polymerization of 310.

Example 3 (Synthesis of Polymer 3) In an autoclave equipped with a stirring device, deionized water 4
00 g of vinyl chloride, 22 g of allyl glycidyl ether, 1 g of ammonium persulfate, and 8 g of polyoxyethylene nonylphenyl ether were charged, and the reaction was started by heating to 55° C. with stirring under a nitrogen gas atmosphere.

Further, 151 g of vinyl chloride and 24 g of allyl glycidyl ether were continuously added over 8 hours, and the temperature was maintained for a further 6 hours to carry out a copolymerization reaction to obtain an emulsion.

This emulsion was left in a freezer at -20°C for a day and night, then thawed in a warm water bath, and the resulting slurry was filtered to form a cake. This cake was dispersed and washed in 1200 g of deionized water and filtered. . This water washing and filtration operation was repeated five times and then dried to obtain 160 g of a copolymer. This contained 87.5% by weight of vinyl chloride, 12.5% by weight of allyl glycidyl ether, and an average degree of polymerization of 320.

Next, 100 g of this copolymer was placed in a reactor equipped with a cooling pipe.
, add 144 g of methanol, 56 g of benzene, 3.2 g of naphthylamine sulfonic acid, and heat at 60°C while stirring.
After reacting for 3 hours, the mixture was cooled, washed five times with 200 g of methanol and twice with deionized water, and filtered and dried to obtain 86 g of a modified copolymer powder (Polymer 3).
This product contains 87.9% by weight of vinyl chloride, 11.1% by weight of allyl glycidyl ether, 0.3% by weight of sulfonic acid group based on the sulfur analysis value, and 0.05% by weight of bound nitrogen.
The average degree of polymerization was 310.

Example 4 (Synthesis of Polymer 4) Deionized water 40°C was added to an autoclave equipped with a stirring device.
0 g, vinyl chloride 14 g, 2-hydroxyethyl methacrylate 2 g, glycidyl methacrylate 2 g, carbon alkylallylsulfosuccinate sodium 2 g
1 g of ammonium 1 persulfate and 4 g of polyoxyethylene nonylphenyl ether were charged, and the reaction was started by heating to 55° C. while stirring in a nitrogen gas atmosphere.

Additionally, 126 g of vinyl chloride, 18 g of 2-hydroxyethyl methacrylate, and 18 g of glycidyl methacrylate.
g, 18 g of alkylaryl sodium sulfosuccinate having an alkyl group having 12 to 13 carbon atoms were continuously added over 8 hours, and the mixture was further maintained at 55° C. for 6 hours to carry out a copolymerization reaction to obtain an emulsion. 50 g of sodium chloride and 500 g of hot water were added to this emulsion, and the resulting slurry was filtered to form a cake.
The dispersion was washed in deionized water and filtered. This water washing and filtration operation was repeated five times and then dried to obtain 160 g of a copolymer. This contains 71.5% by weight of vinyl chloride, 11.5% by weight of 2-hydroxyethyl methacrylate, 11.9% by weight of glycidyl methacrylate, and an alkyl group containing 12 to 12 carbon atoms.
Sodium alkylaryl sulfosuccinate which is 13 5.1
The average degree of polymerization in weight percent was 340.

100 g of this copolymer, 144 g of methanol, 58 g of toluene, and 10 g of triethylamine were added to a reactor equipped with a cooling tube, and the mixture was heated to 60°C while stirring.
After reacting for an hour, it was cooled, washed five times with 200 g of methanol, and twice with deionized water, and filtered and dried to obtain 83 g of a modified copolymer powder (Polymer 4), which contained 68.1 weight of vinyl chloride. %, 2-hydroxyethyl methacrylate 10.5% by weight, glycidyl methacrylate 11.
5% by weight, 4.9% by weight of alkylaryl sodium sulfosuccinate whose alkyl group has 12 to 13 carbon atoms, i.e. 0.9% by weight of sulfonic acid group, 0.43% by weight of nitrogen content,
The average degree of polymerization was 340.

Example 5 (Synthesis of Polymer 5) 40 ml of deionized water was added to an autoclave equipped with a stirring device.
0g, vinyl chloride 120g, ammonium persulfate 1g1
4 g of polyoxyethylene nonyl phenyl ether was charged, and the reaction was started by heating to 55° C. while stirring under a nitrogen gas atmosphere. In addition, glycidyl acrylate 78
g1 2 g of sodium methallylsulfonate was continuously pressurized over a period of 8 hours, and the temperature was further maintained at 55° C. for 6 hours to cause a copolymerization reaction, thereby obtaining an emulsion. To this emulsion, 50 g of sodium chloride and 500 g of hot water were added, and the resulting slurry was filtered to form a cake.
The dispersion was washed in deionized water and filtered. This water washing and filtration operation was repeated five times and then dried to obtain 160 g of a copolymer. As a result, 59.2% by weight of vinyl chloride, 40.3% by weight of glycidyl acrylate, and 0% by weight of sodium methallylsulfonate.
．． A copolymer containing 5% by weight and an average degree of polymerization of 360 was obtained.

100 g of this copolymer, 200 g of methanol, and 2 g of triethylamine were added to a reactor equipped with a cooling tube, heated to 60°C while stirring, and cooled after reacting for 3 hours.
The modified copolymer powder (Polymer 5) was further washed 5 times with 200 g methanol and 2 times with deionized water, filtered and dried.
94 g was obtained, which contained 57.9% by weight of vinyl chloride, 41.5% by weight of glycidyl acrylate, and 0.5% by weight of sodium methallylsulfonate (0.2% by weight of sulfonic acid group).
weight%), nitrogen content of 0.03% by weight, and average degree of polymerization of 350.

Comparative Example 1 (Synthesis of Polymer 6) Polymerization was carried out in the same manner as in Synthesis Example 1, but the amount of monomers was changed to 82 g of vinyl chloride, 36 g of vinyl acetate, and 82 g of additional vinyl chloride.
As a result, 184 g of a copolymer powder containing 85.51 i weight % of vinyl chloride, 14.5 weight % of vinyl acetate, and an average degree of polymerization of 320 was obtained.

100 g of this copolymer, 200 g of methanol, and 3 g of caustic soda were placed in a reactor equipped with a cooling tube, and the temperature was raised to 40°C while stirring, allowed to react for 5 hours, cooled, and 6 g of acetic acid was added to remove any unreacted material. Neutralized caustic soda. This reaction resin was washed four times with 200 g of methanol and twice with 200 g of deionized water, filtered and dried to obtain 85 g of a modified copolymer powder (Polymer 6), which contained 91% of vinyl chloride. It was a modified copolymer with an average degree of polymerization of 310, consisting of 9% by weight, 1.2% by weight of vinyl acetate, and 6.9% by weight of vinyl alcohol.

Comparative Example 2 (Synthesis of Polymer 7) Deionized water 30°C was placed in an autoclave equipped with a stirring device.
0g, vinyl chloride 73g, vinyl acetate 54g, di(2-
0.3 g of ethylhexyl) peroxydicarbonate and 2 g of partially saponified polyvinyl alcohol were charged, the temperature was raised to 70°C while stirring under a nitrogen gas atmosphere, and the reaction was started. Furthermore, 73 g of vinyl chloride was continuously pressurized over a period of 5 hours. A copolymerization reaction was carried out.

Autoclave internal pressure is 0.5kg/cm2G after 8 hours.
The residual pressure was released and the mixture was cooled, washed twice with 1000 g of deionized water, filtered and dried to obtain 158 g of copolymer powder. This copolymer was composed of 74.6% by weight of vinyl chloride and 25.4% by weight of vinyl acetate and had an average degree of polymerization of 420.

In a reactor equipped with a cooling tube, 100 g of this copolymer, 170 g of methanol, 30 g of toluene, 10 g of caustic soda were charged, and the temperature was raised to 45°C with stirring to react for 5 hours. After cooling, 20 g of acetic acid was added to remove any unreacted material. Neutralized caustic soda. This reaction product was washed six times with 200 g of methanol and twice with 200 g of deionized water, filtered and dried to obtain 64 g of a modified copolymer powder (Polymer 7), which contained 86.7 g of vinyl chloride. It was a modified copolymer with an average degree of polymerization of 380, consisting of 1.1% by weight of vinyl acetate and 12.2% by weight of vinyl alcohol.

Measurement of magnetic performance: 7.6 g of each modified copolymer (Polymer 1 to 7) obtained
, )-toluene 10.1g, methyl ethyl ketone 10
．． Put 1 g of methyl isobutyl ketone and 10.1 g of methyl isobutyl ketone into a flask and dissolve at 50°C for 1 hour, then add 30 g of each of the following magnetic powders A to C while mixing with an Eiger mill.
Kneaded for hours. Furthermore, add 1.8 g of Coronate (manufactured by Nippon Polyurethane Co., Ltd.) and knead for 5 minutes.
It was suction-filtered through a micron filter and used as a magnetic paint.

This was placed on a 16 μm thick polyester film with 6 μm
It was coated to a thickness of m, subjected to magnetic field orientation treatment, and dried.

The magnetic properties of the magnetic tape made in this way were investigated. The results were as shown in the table below.

The gloss was measured using a gloss meter manufactured by Murakami Color Giken.
The reflectance was measured, and the Br and squareness ratio were measured using a vibrating sample magnetometer manufactured by Toei Kogyo.

Magnetic powder A: 7-Fe2O of 2h”/H.

Magnetic powder B: 40ta”7g of Go-7-Fe20
s Magnetic powder C: 50 m''/H metal powder [Effects of the invention] The magnetic recording medium according to the present invention has the following characteristics: (1) Since the ferromagnetic powder has good dispersibility, it is possible to obtain a medium with high residual magnetic flux density and squareness ratio.

■ Good gloss and durability with little powder loss.

Claims (1)

[Claims] 1. A magnetic layer in which fine ferromagnetic powder is dispersed in a binder resin mainly composed of an amine-modified vinyl chloride copolymer having sulfonic acid groups is placed on a support. A magnetic recording medium formed by forming a magnetic recording medium. 2. The vinyl chloride copolymer contains (a) 60 to 95% by weight of vinyl chloride units, (b) 0.02 to 0.6% by weight as bonded nitrogen, and (c) 0.05% as sulfonic acid group. 2. The magnetic recording medium according to claim 1, comprising .about.1.0% by weight and some amount of other vinyl units added as necessary.