JP3401352B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium and, in particular, has been improved by using a special copolymer mainly composed of vinyl chloride, which has excellent performance as a binder for ferromagnetic powder. The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art In magnetic recording media such as magnetic tapes, magnetic cards and floppy disks, a coating film (magnetic layer) comprising a magnetic powder and a binder (synthetic resin) is generally provided on the surface of a support such as a polyester film. Made by. In recent years, in order to increase the coercive force and the maximum saturation magnetization amount, and to improve the SN ratio and recording density, magnetic powders are more miniaturized than ever before and have a large specific surface area and a metal magnet having a very large magnetic moment. Powder has come into use. As a result, in order to uniformly disperse the magnetic powder in the paint and form a smooth and highly filled magnetic layer to improve the performance as a magnetic recording medium, the dispersion performance of the binder is critical. It becomes an important factor. However, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers and nitrocellulose, which are usually used as synthetic resin binders, lack the dispersibility of magnetic powders and are expected to have expected performance. Can't exert. In addition, a surfactant may be used to improve the dispersibility, but when used in a sufficient amount, bleeding is likely to occur from the magnetic layer, which lowers the durability and contaminates the magnetic head. There was a drawback.

[0003]

Therefore, the present invention is
High dispersibility for high-performance finely divided magnetic powder,
We have developed a copolymer for binders that can be highly filled without the need to add surfactants that pollute the magnetic head.
This is intended to provide a magnetic recording medium exhibiting excellent surface smoothness and durability and excellent magnetic characteristics.

[0004]

The present invention has solved the above-mentioned problems, and the magnetic recording medium of the present invention is a magnetic recording medium in which ferromagnetic fine powder is dispersed in a binder on a non-magnetic support. In a magnetic recording medium having a layer, the binder comprises (a) a vinyl chloride unit, (b) a vinyl acetate unit, and (c) a vinyl-based monomer unit having a hydroxyl group-containing organic group as a side chain as an essential constituent component. The vinyl chloride-based copolymer obtained by copolymerization in the presence of a chain transfer agent having an SH group is used as a main component. That is, as a result of earnest studies to solve the above-mentioned problems, the present inventors copolymerized vinyl chloride monomer, vinyl acetate monomer and vinyl monomer having a hydroxyl group-containing organic group in the presence of a chain transfer agent having an SH group. The inventors of the present invention have found that when the copolymer obtained as described above is used as the main component of the binder, the dispersion performance in the ferromagnetic fine powder and the durability performance of the magnetic layer are simultaneously improved, and the present invention was completed.

The present invention will be described in detail below. The copolymer used as the main component of the binder in the present invention essentially comprises a vinyl chloride unit, a vinyl acetate unit and a vinyl monomer unit having a hydroxyl group-containing organic group as a side chain as described above. Of these units, the vinyl chloride unit of (a) unit imparts toughness and high surface hardness to the coating film, but when the amount thereof decreases, the strength of the magnetic coating film decreases, and the polyurethane resin described below is used. The compatibility with and deteriorates, and when it increases, the solubility in the solvent decreases, the viscosity of the magnetic coating increases, and the dispersibility decreases.
It is preferably from 60 to 95% by weight. The vinyl acetate unit as the unit (b) improves the solvent solubility of the copolymer and lowers the paint viscosity, but when the amount decreases, the solubility in the solvent decreases and the magnetic paint viscosity increases, resulting in dispersion. Since the properties of the copolymer decrease and the greater the amount, the strength and durability of the magnetic coating film decrease. Therefore, it is preferably 2 to 10% by weight in the copolymer.

The vinyl monomer unit having a hydroxyl group-containing organic group as a side chain of (c) unit reacts with a polyisocyanate curing agent to give a coating film which is tough and has good durability and adhesion. When the amount of the polyisocyanate-based curing agent is reduced, the reactivity is decreased and the durability is deteriorated, and when the amount is increased, the glass transition temperature of the copolymer is decreased and the durability is deteriorated, or the polyurethane is deteriorated. When the resin is used in combination, the compatibility with the resin also decreases, so it is preferably 2 to 30% by weight in the copolymer. Examples of the monomer for introducing the (c) unit include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene. Glycol mono (meth) acrylate, glycerol mono (meth) acrylate, 3-
Examples thereof include chloro-2-hydroxypropyl (meth) acrylate, glycerin monoallyl ether, hydroxyethyl vinyl ether, ethylene glycol monoallyl ether, hydroxybutyl vinyl ether, (meth) allyl alcohol, and N-methylol (meth) acrylamide.

In addition to these, a copolymerizable monomer can be used if necessary, and examples thereof include vinyl propionate, vinyl versatate, styrene, α-methylstyrene, acrylonitrile and methyl (meth) acrylate. , Alkyl (meth) acrylates such as ethyl (meth) acrylate, acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, vinylidene chloride and the like. The amount of the monomer unit introduced by these monomers can be in the range of 10% by weight or less in the copolymer as long as the effect of the present invention is not impaired.

A chain transfer agent having an SH group is used in the production of a copolymer composed of a vinyl chloride monomer, a vinyl acetate monomer and a vinyl monomer having a hydroxyl group-containing organic group. The chain transfer agent is t- Examples include butyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, n-tetradecyl mercaptan, n-octadecyl mercaptan, and 3-ethoxypropanethiolethylthioglycolate, but n-dodecyl mercaptan and n-octyl mercaptan are examples. It is preferable. The amount of these chain transfer agents used may be 0.02 to 1% by weight in terms of sulfur content based on the total amount of the monomers, but is preferably 0.05 to 0.5% by weight.

If the average degree of polymerization of the copolymer used in the present invention is too low, the magnetic coating becomes brittle and its physical strength is lowered, and the durability of magnetic tapes is also lowered. If the value is too high, the viscosity of the coating material at a predetermined concentration becomes high, the workability is significantly deteriorated, and the handling becomes difficult. Since the average degree of polymerization changes depending on the presence of chain transfer agents and organic solvents, the polymerization temperature, etc., these factors should be selected appropriately.
It is preferably in the range of 400. A chain transfer agent containing no sulfur (eg trichlene, diisobutylene, etc.) can also reduce the average degree of polymerization, but it is surprisingly effective to use a chain transfer agent having an SH group for dispersing the ferromagnetic fine powder. It was found to be.

Such a copolymer can be produced by a general suspension polymerization method, emulsion polymerization method, solution polymerization method, bulk polymerization method or the like. Examples of the polymerization initiator used in the production of the copolymer include persulfates such as potassium persulfate and ammonium persulfate, water-soluble types such as hydrogen peroxide and t-butyl hydroperoxide, or benzoyl peroxide and lauryl peroxide. Oxide, cumene hydroperoxide, cumyl peroxy neodecanoate, dibutyl peroxide, t-hexyl peroxypivalate, diisopropyl peroxy carbonate, di-2-ethylhexyl peroxy carbonate,
Di-2-ethoxyethyl peroxydicarbonate, t
Examples include oil-soluble types such as butyl peroxymaleic acid and azobisisobutyronitrile. When copolymerizing at low temperature, it is preferable to use a redox catalyst in combination with a reducing agent, and the above-mentioned radical generating source and a reducing agent such as acidic sodium sulfite, L-ascorbic acid, sodium formaldehyde sulfoxylate, glucose and sucrose. , And trace amounts of ferrous salt are preferred.

As the suspension stabilizer, polyvinyl alcohol, partially saponified polyvinyl acetate, methyl cellulose,
Cellulose derivatives such as hydroxypropyl cellulose and carboxymethyl cellulose, polyvinylpyrrolidone,
Polyacrylamide, maleic acid-styrene copolymer,
Examples thereof include synthetic polymers such as maleic acid-methyl vinyl ether copolymer, and natural polymers such as starch and gelatin. Examples of the emulsifier include anionic emulsifiers such as alkyl or alkylallyl sulfate, alkyl or alkylallyl sulfonate, dialkyl sulfosuccinate, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene carboxylic acid ester. And nonionic emulsifiers such as

In the polymerization, the above-mentioned monomers, chain transfer agents, polymerization initiators, suspension stabilizers, emulsifiers, etc. may be added to the polymerization system all at once at the start of the polymerization. It can also be added in portions. In the case of emulsion polymerization,
According to a known salting-out method after the polymerization, sodium chloride, calcium chloride, or after adding an aqueous solution of an inorganic salt such as sodium sulfate, or after aggregating the particles by adding a water-soluble organic solvent, etc., filtered, washed with water, Just dry.

When the above copolymer is used as a binder resin in the production of a magnetic coating material, other resins may be used in an amount equal to or less than an equal amount, if necessary, as the resins which can be used in combination, a polyurethane resin, Nitrocellulose, polyester resin, epoxy resin, polyamide resin, phenol resin,
Examples include various resins such as polymers or copolymers such as alkyd resins and polyvinyl butyral resins. Among these, polyurethane resin is preferable.

In addition to this, it is desirable to use a polyisocyanate curing agent in combination, and as this curing agent, Coronate L [trade name of Nippon Polyurethane Industry Co., Ltd.], Dismodur L [trade name of Bayer Co.] Examples thereof include trifunctional isocyanates, urethane prepolymers having isocyanate groups at both ends, and the like. The amount of these curing agents used is preferably 5 to 40 parts by weight based on 100 parts by weight of the binder resin including the resins used in combination.

The ferromagnetic fine powder used in the present invention includes γ-Fe ₂ O ₃ , Fe ₃ O ₄ and their adsorbed or doped cobalt ions, CrO ₂ , and Fe, Co, Fe-.
Examples thereof include acicular fine particles of metal or alloy containing Co, Ni and the like, and other various conventionally known magnetic powders. The mixing ratio of the ferromagnetic powder and the binder resin is preferably 8 to 50 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic powder. In order to uniformly disperse the ferromagnetic fine powder and the binder resin, a lubricant, an abrasive, an antistatic agent, a dispersion aid, a rust preventive, etc., which are generally used in the past, are added, and a coating medium is further added. As methyl ethyl ketone,
The use of various organic solvents other than methyl isobutyl ketone, cyclohexanone, toluene and the like may be the same as the conventional one, and there is no particular limitation in these points.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate and polycarbonate, non-magnetic metals, ceramics and the like are used, and the form is used as a film, tape, sheet, plate or the like. A known method may be used as a coating means for forming the magnetic layer on the support, and a high-performance magnetic recording medium intended by the present invention can be obtained by appropriately performing smoothing treatment such as calendering treatment. To be

[0017]

EXAMPLES Next, examples of synthesizing a copolymer, specific examples using this copolymer, and comparative examples will be given, but the present invention is not limited to the scope of these examples. In addition, part and% in an example show a weight part and weight%, respectively. Moreover, each monomer unit in the copolymer was quantified by the following method. Vinyl chloride unit: A sample is burned in oxygen using a platinum catalyst, the generated hydrochloric acid is absorbed in water and titrated with a silver nitrate solution. Vinyl acetate unit: quantified from C = O / C-Cl absorption ratio by FT-IR. Vinyl-based monomer unit having a hydroxyl group-containing organic group: FT-
Quantify by IR from C-OH / C-Cl absorption ratio.

Synthesis Example 1 (Synthesis of Polymer 1) A polymerization vessel equipped with a stirrer, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 940 parts of deionized water and 1,140 of methanol were added.
Parts, 394 parts of vinyl chloride, 15 parts of vinyl acetate, 44 parts of hydroxypropyl acrylate, 1 part of azobisisobutyronitrile, 1.5 parts of partially saponified polyvinyl alcohol and n
-Prepare 10 parts of dodecyl mercaptan and mix with stirring.
The reaction is started by heating to ℃
Parts, 46 parts of vinyl acetate and 138 parts of hydroxypropyl acrylate were continuously added over 8 hours to carry out a polymerization reaction.
Since the internal pressure of the polymerization vessel reached 0.5 kg / cm ² (gauge pressure) after 12 hours, the residual pressure was released and cooled, washed with 1,500 parts of deionized water three times, filtered, and dried at 50 ° C. to obtain a copolymer. (Polymer 1) 1,090 parts were obtained. The polymer 1 thus obtained had a vinyl chloride unit of 79.3%, a vinyl acetate unit of 3.4%, a hydroxypropyl acrylate unit of 16.0%, a sulfur content of 0.14% and an average degree of polymerization of 310.

Synthesis Example 2 (Synthesis of Polymer 2) Synthetic except that 5 parts of octyl mercaptan was used in place of 10 parts of the chain transfer agent n-dodecyl mercaptan, and hydroxyethyl methacrylate was used in place of the polymerization monomer hydroxypropyl acrylate. Polymerization was carried out in the same manner as in Example 1, followed by washing, filtration and drying to obtain a copolymer (Polymer 2) 1,1
I got 00 copies. This polymer 2 has a vinyl chloride unit of 77.7
%, Vinyl acetate unit 3.1%, hydroxyethyl methacrylate unit 18.5%, sulfur content 0.07%, average degree of polymerization 300.

Synthesis Example 3 (Synthesis of Polymer 3) A polymerization vessel equipped with a stirrer, a thermometer and a nitrogen gas inlet was purged with nitrogen, and then 2,000 parts of deionized water, 25 parts of sodium lauryl sulfate and polyoxyethylene octylphenyl ether. 20 parts, t-butyl hydroperoxide 2.7
Parts, 6 parts sodium carbonate, 10 parts dodecyl mercaptan,
Charge 164 parts of vinyl chloride, 10 parts of vinyl acetate and 20 parts of hydroxypropyl acrylate, heat to 65 ° C with stirring to start the reaction, and add 636 parts of vinyl chloride, 40 parts of vinyl acetate and 130 parts of hydroxypropyl acrylate. 8
A polymerization reaction was carried out by continuously adding it over a period of time. The pressure inside the polymerization vessel is
After 12 hours, the pressure became 0.5 kg / cm ² (gauge pressure), so the residual pressure was released, 3,000 parts of 50% calcium chloride aqueous solution was added to raise the temperature, and the mixture was stirred at 80 ° C. for 1 hour to precipitate the copolymer. . Wash the precipitated copolymer 3 times with 3,000 parts of deionized water,
It was filtered and dried at 50 ° C. to obtain 890 parts of a copolymer (polymer 3). This polymer 3 had a vinyl chloride unit of 77.7%, a vinyl acetate unit of 4.3%, a hydroxypropyl acrylate unit of 16.3%, a sulfur content of 0.17% and an average degree of polymerization of 370.

Synthesis Example 4 (Synthesis of Polymer 4) A polymerization vessel equipped with a stirrer, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 2,000 parts of methanol, 10 parts of diisopropyl peroxydicarbonate, 2 parts of dodecyl mercaptan, and chloride. Charge 180 parts of vinyl, 14 parts of vinyl acetate, 7 parts of hydroxypropyl acrylate and stir at 50 ℃
The reaction was started by heating to 700 parts of vinyl chloride,
56 parts of vinyl acetate and 43 parts of hydroxypropyl acrylate were continuously added for 8 hours to carry out a polymerization reaction. The internal pressure of the polymerization vessel reached 0.2 kg / cm ² (gauge pressure) after 12 hours, so the residual pressure was released, washed with 2,000 parts of methanol 3 times and with 3,000 parts of deionized water 2 times, filtered, and heated to 50 ° C. After drying, 620 parts of a copolymer (polymer 4) was obtained. This polymer 4 had a vinyl chloride unit of 89.2%, a vinyl acetate unit of 4.3%, a hydroxypropyl acrylate unit of 6.2%, a sulfur content of 0.05% and an average degree of polymerization of 210.

Synthesis Example 5 (Synthesis of Polymer 5) A polymerization vessel equipped with a stirrer, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 940 parts of deionized water and 1,140 of methanol were added.
Parts, vinyl chloride 188 parts, vinyl acetate 7 parts, hydroxyethyl acrylate 40 parts, partially saponified polyvinyl alcohol 1.5 parts, diisopropyl peroxydicarbonate
1.5 parts and 24 parts of octyl mercaptan were charged and heated to 65 ° C with stirring to start the reaction.
676 parts, 29 parts of vinyl acetate and 260 parts of hydroxyethyl acrylate were continuously added for 8 hours to carry out a polymerization reaction. Since the internal pressure of the polymerization vessel reached 2.5 kg / cm ² (gauge pressure) after 12 hours, the residual pressure was released and cooled, washed with 1,500 parts of deionized water three times, filtered, and dried at 50 ° C. to obtain a copolymer. (Polymer 5)
I got 840 copies. This polymer 5 has a vinyl chloride unit of 68.0
%, Vinyl acetate unit 2.3%, hydroxypropyl acrylate unit 27.1%, sulfur content 0.34%, average degree of polymerization 270.

Synthesis Example 6 (Synthesis of Polymer 6) Polymerization was carried out in the same manner as in Synthesis Example 1 except that trichlene was used in place of the chain transfer agent n-dodecyl mercaptan,
It was washed, filtered and dried to obtain 1,050 parts of copolymer (Polymer 6). This polymer 6 had a vinyl chloride unit of 81.9%, a vinyl acetate unit of 3.0%, a hydroxypropyl acrylate unit of 15.1%, and an average degree of polymerization of 300.

Synthesis Example 7 (Synthesis of Polymer 7) Polymerization was carried out in the same manner as in Synthesis Example 3 except that diisobutylene was used instead of the chain transfer agent n-dodecyl mercaptan, salting out was carried out in the same manner, and washing, After filtration and drying, 830 parts of a copolymer (polymer 7) was obtained. This polymer 7 had a vinyl chloride unit of 79.6%, a vinyl acetate unit of 4.5%, a hydroxypropyl acrylate unit of 15.9%, and an average degree of polymerization of 350.

Synthesis Example 8 (Synthesis of Polymer 8) As initial charge monomers, instead of 394 parts of vinyl chloride, 15 parts of vinyl acetate and 44 parts of hydroxypropyl acrylate, 511 parts of vinyl chloride and 180 parts of vinyl acetate were continuously added. Polymerization was carried out in the same manner as in Synthesis Example 1, except that 566 parts of vinyl chloride, 46 parts of vinyl acetate, and 512 parts of vinyl chloride were used instead of 138 parts of hydroxypropyl acrylate as a monomer, and the mixture was washed, filtered, and dried. Thus, 1,095 parts of a copolymer (polymer 8) was obtained. This polymer 8 had a vinyl chloride unit of 85.2%, a vinyl acetate unit of 13.3%, a sulfur content of 0.24% and an average degree of polymerization of 350.

Examples 1 to 5 and Comparative Examples 1 to 3 Preparation of Magnetic Paint Liquid A Polymer 1 to 8 30 parts Magnetic powder (Fe-Co-Ni) specific surface area 50 m ² / g 300 parts Polyurethane resin [N-2304: Trade name of Nippon Polyurethane Industry Co., Ltd.] 20 parts Silicone oil (dimethylpolysiloxane) 3 parts Methyl ethyl ketone 300 parts Methyl isobutyl ketone 300 parts Toluene 300 parts The above ingredients are mixed for 90 minutes with a mixer and further kneaded with an Eiger mill for 3 hours. A coating liquid A was obtained. Liquid B Liquid A 1,250 parts Polyisocyanate [Coronate L: trade name of Nippon Polyurethane Industry Co., Ltd.] 6 parts The above components were mixed and dispersed for 90 minutes with a mixer to obtain a coating liquid B.

Preparation of Magnetic Tape The above coating liquid B was applied on a polyester film to a thickness of 5 μm, subjected to magnetic field orientation treatment and dried, and then surface treated using a super calender to produce a magnetic tape.

Measurement of Physical Properties The viscosity of the coating liquid A obtained as described above, the coating properties of the magnetic tape and the magnetic properties were examined. The results are as shown in Table 1. In addition, the measurement of each characteristic was performed as follows. a. Viscosity of coating liquid A The viscosity of the prepared liquid A was measured with an E-type viscometer (initial viscosity). b. A 60-degree reflectance of the coated surface before calendering was compared with that of a standard glass plate using a gloss gloss meter (manufactured by Murakami Color Research Institute). c. Both the orientation degree and the squareness ratio were measured using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.). d. Durability The created magnetic tape is left in a constant temperature and humidity room at 65 ° C and 90% relative humidity for 168 hours, then a load of 100 g is applied, it is brought into contact with a rotating drum with abrasive paper, and it is rotated 1,000 times at 150 rpm, The degree to which the magnetic coating film adhered to the abrasive paper was visually evaluated on a 4-point scale. ◎: Abrasive paper is not stained, ○: Very slightly stained, △:
There is some dirt, ×: There is much dirt

[0029]

[Table 1]

[0030]

EFFECTS OF THE INVENTION According to the present invention, a magnetic paint having highly dispersed fine particles of ferromagnetic powder and having a viscosity suitable for coating work can be obtained. By using the paint, the smoothness and durability of the coating film surface can be obtained. Provided is a novel magnetic recording medium having good properties and excellent magnetic characteristics.

Continuation of the front page (56) Reference JP-A-6-322207 (JP, A) JP-A-58-177524 (JP, A) JP-A-5-182174 (JP, A) JP-A-56-3339 (JP , A) JP 56-77930 (JP, A) JP 6-9809 (JP, A) JP 8-153320 (JP, A) JP 5-334655 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/702

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer comprising ferromagnetic fine powder dispersed in a binder on a non-magnetic support, wherein the binder is (a) vinyl chloride unit and (b) vinyl acetate. A vinyl monomer unit having a hydroxyl group-containing organic group as a unit and (c) a side chain is an essential constituent component, S
A magnetic recording medium comprising a vinyl chloride-based copolymer obtained by copolymerization in the presence of a chain transfer agent having an H group as a main component. 2. The copolymer is (a) unit 60 to 95% by weight, (B) unit 2 to 10% by weight, (C) unit 2 to 30% by weight.
The magnetic recording medium according to claim 1, which is a vinyl chloride-based copolymer having an average degree of polymerization of 150 to 400 and containing a slight amount of other vinyl units, if necessary.