JPH0628658A - Binder for magnetic recording medium and magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a binder for a magnetic recording medium having high dispersibility and excellent preservability over a long period of time and a magnetic recording medium. CONSTITUTION:This binder for a magnetic recording medium contains a copolymer of a vinyl monomer with other copolymerizable component and a vinyl compd. having a chemical structure which ensures high dispersibility, e.g. vinyl phenol or its deriv. is used as the vinyl monomer. This magnetic recording medium has a magnetic layer or a nonmagnetic layer using this binder. Dehydrochlorination is not caused and this magnetic recording medium is excellent in stability and preservability over a long period of time.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a binder of a ferromagnetic powder for a magnetic recording medium, specifically a binder for a magnetic layer of a magnetic recording medium, a binder for a non-magnetic layer (intermediate layer) and a back layer. Binder,
The present invention relates to a binder suitable as a binder for a protective layer and a magnetic recording medium using the binder.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks and the like. In a magnetic recording medium, a magnetic layer in which ferromagnetic powder is dispersed in a binder (binder) is laminated on a non-magnetic support. The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. That is, in audio tapes for recording and reproducing music, a higher level of original sound reproduction capability is required. Further, the video tape is required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability. In addition to having such excellent electromagnetic conversion characteristics, the magnetic recording medium is required to have good running durability as described above. Then, in order to obtain good running durability, an abrasive and a lubricant are usually added to the magnetic layer.

However, in order to obtain excellent running durability with the abrasive, it is necessary to increase the addition amount to some extent, which reduces the content of the ferromagnetic powder.
Further, when an abrasive having a large particle size is used in order to obtain excellent running durability, the abrasive tends to excessively project on the surface of the magnetic layer. Therefore, the improvement of running durability by the abrasive often causes the above-mentioned deterioration of the electromagnetic conversion characteristics, which is a problem. When the running durability is improved by the lubricant, it is necessary to increase the addition amount of the lubricant, so that the binder is likely to be plasticized and the durability of the magnetic layer tends to decrease.

Further, in order to improve the durability and electromagnetic conversion characteristics, the binder, which is one of the main components of the magnetic layer, naturally also plays an important role. Conventionally used vinyl chloride-based resins, cellulose-based resins, urethane-based resins, acrylic-based resins and the like have a problem that the wear resistance of the magnetic layer is poor and the running system members of the magnetic tape are contaminated. As a method of improving such a problem, a method of increasing the hardness of the magnetic layer by using a hard binder is used. However, when the hardness of the magnetic layer is increased, the brittleness of the magnetic layer becomes remarkable, and there are problems that dropout occurs due to contact with the magnetic head and that the still characteristics are deteriorated.

Further, the fine magnetic powder to increase the magnetic force of the ferromagnetic powder or increase the packing density of the ferromagnetic powder brings about an increase in the cohesive force due to an increase in the magnetic force or the specific surface area. There is a problem that the dispersion is lowered and sufficient magnetic properties and surface properties cannot be obtained. In addition, a nonmagnetic layer (intermediate layer) is provided between the magnetic layer and the nonmagnetic support.
In the magnetic recording medium having the above, the dispersibility of the abrasive or carbon black is inferior with the binder conventionally used as a binder for dispersing the abrasive or the carbon black, and the magnetic layer positioned on the smooth upper layer is good. No good surface property was obtained.

[0006]

Although vinyl chloride copolymers are widely used as binders for magnetic recording media, vinyl chloride copolymers have high dispersibility of magnetic materials and at the same time contribute to durability. Although it is also large, vinyl chloride itself does not have a polar part, so by introducing a polar group into the raw material such as polyurethane used with vinyl chloride copolymer, it is possible to disperse with the hardness and abrasion resistance of the binder. It was done to improve the sex.

Further, it has been proposed in JP-A-57-44227 to introduce a polar group into a vinyl chloride copolymer to improve the dispersibility. PVC is the publication - vinyl acetate - vinyl on OH groups of the vinyl alcohol alcohol copolymer by introducing a -SO ₃ M, hydrophilic group group containing such -COOH or -SO ₃ M, vinyl copolymerization chloride It is described that the dispersibility of the coalescence is increased.

However, since such a copolymer has vinyl chloride, it has a problem that generation of hydrochloric acid due to hydrolysis of vinyl chloride is unavoidable during long-term use. When vinyl chloride hydrolyzes to generate hydrochloric acid, it adversely affects the ferromagnetic powder and also hydrolyzes the ester portion of the polyurethane used with the vinyl chloride copolymer to lower the molecular weight,
Alternatively, there is a problem that unsaturated bonds are generated from the vinyl chloride copolymer by dehydrochlorination to soften the magnetic layer and reduce the durability.

Further, these vinyl chloride copolymers are not sufficient in heat resistance, and further, since they contain chlorine, there is a problem that hydrochloric acid gas is generated during incineration.

The present invention provides a binder for a magnetic recording medium, which has excellent long-term storage stability, durability, dispersibility, and electromagnetic conversion characteristics, and a magnetic recording medium.

[0011]

The present invention provides a binder for a magnetic recording medium containing a copolymer of a vinyl monomer and another copolymerizable component, wherein the vinyl monomer is vinylphenol or its derivative. In a magnetic recording medium provided with a binder for a medium, and a magnetic layer obtained by dispersing a ferromagnetic powder in the binder or a non-magnetic layer obtained by dispersing a non-magnetic powder and a binder, and a back layer,
A magnetic recording medium in which the binder contains a copolymer of a vinyl monomer which is vinylphenol or a derivative thereof and another copolymerizable component.

Further, in a magnetic recording medium in which a lower magnetic layer or a lower nonmagnetic layer is provided on at least one surface of a nonmagnetic support and an upper magnetic layer is provided thereon, at least the magnetic layer or the nonmagnetic layer is provided. The first layer is a magnetic recording medium in which the binder for dispersing the ferromagnetic powder or the non-magnetic powder contains a copolymer composed of vinyl phenol or a vinyl monomer which is a derivative thereof and another copolymerizable component.

That is, the present invention is a binder comprising a copolymer containing vinylphenol or a derivative thereof as a monomer component, and the following are examples of polyvinylphenol and a derivative thereof.

[0014]

[Chemical 1]

The content in the copolymer is 10 to 90 mol.
%, More preferably 20 to 70 mol%. If it is less than 10 mol%, the effect of heat resistance and durability is small, and if it is more than 90 mol%, it becomes brittle. Monomers copolymerizable with vinylphenol of the present invention include vinyl acetate, carboxylic acid vinyl esters such as vinyl propionate, methyl vinyl ether, isobutyl vinyl ether, cetyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth). )
Acrylate, stearyl (meth) acrylate, 2-
Hydroxyethyl (meth) acrylate, diethyl maleate, butylbenzyl maleate, unsaturated carboxylic acid esters such as dimethyl itaconic acid, styrene, aromatic vinyl such as α-methylstyrene, olefins such as ethylene, propylene, butadiene and isoprene, Maleic acid, (meth) acrylic acid, acid phosphoxyethyl (meth) acrylate, ethyl sulfonate (meth) acrylate, styrene sulfonic acid, alkali metal salts or ammonium salts thereof, vinyl alcohol, allyl glycidyl ether, glycidyl (meth) Examples thereof include polar group-containing monomers such as acrylate.

The degree of polymerization is 100 to 2000, preferably 2
It is preferably from 00 to 600, and when the degree of polymerization is low, the mechanical strength and dispersibility decrease, and when it is too high, the viscosity increases and the dispersibility decreases. The glass transition point is 20 to 12
0 ° C. is preferable, and if the glass transition point is low, blocking tends to occur, which causes a problem in the manufacturing process. If it is too high, the calender moldability is deteriorated and the smoothness and electromagnetic conversion characteristics are deteriorated. In the present invention, the binder for the magnetic recording medium is used because it can be used in any of the magnetic layer, non-magnetic (intermediate) layer, back layer and protective layer of the magnetic recording medium.

Further, various synthetic resins can be used together in each magnetic layer or non-magnetic layer. Examples thereof include ethylene / vinyl acetate copolymers, cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, epoxy resins, and phenoxy resins. These can be used alone or in combination.

When other synthetic resin is used in combination, the urethane contained in the magnetic layer is preferably contained in the binder in an amount of 10% by weight or more, more preferably 20% by weight or more. . The vinyl resin is preferably contained in the binder in an amount of 80% by weight or less, more preferably 70% by weight or less.

In the case of using a polyurethane which exhibits a great effect in improving the properties in combination with a vinyl resin,
The weight average molecular weight of polyurethane is preferably from 1 to 150,000. When it is larger than this, the viscosity is high and the dispersibility is lowered, and when it is smaller than this, the mechanical strength is low and the durability is deteriorated.

As the polyurethane, polyurethane which is a reaction product of polyol and polyisocyanate as main raw materials can be used. That is, a polyurethane produced from a raw material containing a polyol and a polyisocyanate as main raw materials and containing various additives such as a chain extender, and as the polyol, those having an aliphatic polyol are particularly preferable. Is preferably a polyol having an OH group at the end of a hydrocarbon chain having a molecular weight of 500 to 5,000, and the OH group may be at a position other than the end of the carbon chain. The preferable range of the molecular weight is 800 to 3,000. When the molecular weight is small, the dispersibility is not preferable, and when the molecular weight is too large, the solubility in a solvent is lowered and the dispersibility is lowered. The carbon chain may have a linear or branched structure, and the carbon chain may be saturated,
Any of unsaturated can be used. When unsaturated polyolefin polyol or polybutadiene polyol is used as the aliphatic polyol, it is preferable that the unsaturated double bond is small.

The content of the polyolefin polyol in the polyurethane is preferably 20 to 90% by weight, and when the content is small, the dispersibility is not preferable and the effect of durability is small. On the other hand, if the amount is too large, the glass transition temperature (Tg) decreases,
It becomes difficult to adjust the physical properties of the resulting composition. Further, as the polyisocyanate, aromatic polyisocyanates such as MDI (4,4′-diphenylmethane diisocyanate), TDI (tolylene diisocyanate), and XDI (xylylene diisocyanate) are preferable. Since the polyolefin polyol segment is soft, the physical properties of the aromatic diisocyanate can be adjusted more easily.

Additives such as a chain extender may be added in addition to the polyol and polyisocyanate. The chain extender may be ethylene glycol, 1,4-butanediol,
Glycols such as 2,3-butanediol, dihydroxyethyl ether of bisphenol A and hydroquinone dihydroxyethyl ether, and diamines such as diphenylmethanediamine and m-phenylenediamine can be used. The terminal of the molecule of the polyurethane is preferably an OH group terminal. The OH group reacts with the isocyanate curing agent in the magnetic layer to crosslink to strengthen the magnetic layer coating film. Further, the glass transition temperature (Tg) of polyurethane is -20 to +5.
0 ° C is preferred. When the glass transition temperature is low, the magnetic coating film before curing has a low blocking property, and when it is high, it becomes brittle, which is not preferable in terms of durability.

The binder comprising a copolymer of the vinyl monomer of the present invention and another copolymerizable component is -SO.
_{3 M, -OSO 3 M, -COOM} , -PO 3 M '2, -O
^{_{PO 3 M '2, -NR 2}} , -N + R 3 X -, -N + R 2 R
^{_{'SO 3 -, -N + R}} 2 R' COO - ( however, M is hydrogen, alkali metal, alkaline earth metal, ammonium salts, M ^'is hydrogen, an alkali metal, alkaline earth metal, ammonium salts, an alkyl group, R, R ^'is an alkyl group, X can improve dispersibility by containing at least one polar group selected from a halogen), the amount of these polar groups Is preferably contained in an amount of 1 × 10 ⁻⁶ to 2 × 10 ⁻³ equivalents per 1 g of the polymer. Two
× 10 ^-3 to rise more than the viscosity equivalent, it tends to decrease dispersibility and dispersibility less than 1 × 10 ^-6 eq tends to decrease.

Further, a curing agent such as a polyisocyanate compound can be used together with the binder of the present invention.
Examples of the polyisocyanate compound include a reaction product of 3 mol of tolylene diisocyanate and 1 mol of trimethylol propane (eg, Desmodur L-75 (manufactured by Bayer)), diisocyanate 3 such as xylylene diisocyanate or hexamethylene diisocyanate. Mole reaction product of 1 mole of trimethylolpropane, buret addition compound with 3 moles of hexamethylene diisocyanate, isocyanurate compound of 5 moles of tolylene diisocyanate, isocyanurate addition of 3 moles of tolylene diisocyanate and 2 moles of hexamethylene diisocyanate Mention may be made of the compounds, polymers of isophorone diisocyanate and diphenylmethane diisocyanate. The polyisocyanate compound contained in the magnetic layer is preferably contained in the binder in an amount of 10 to 50% by weight, more preferably 20 to 40% by weight.

Further, when the curing treatment is carried out by electron beam irradiation, a compound having a reactive double bond (eg urethane acrylate) can be used. The total weight of the resin component and the curing agent (that is, the binder) is preferably in the range of usually 15 to 40 parts by weight, more preferably 20 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder. Is. The ferromagnetic powder used in the magnetic recording medium of the present invention is a ferromagnetic iron oxide, a cobalt-containing ferromagnetic iron oxide or a ferromagnetic alloy powder having an S _BET specific surface area of 40 m ² / g or more (preferably 50 m ² / g or more). ), The crystallite size is 35
nm or less, preferably 25 nm or less. As the ferromagnetic powder, Fe, Ni, Fe-Co, Fe-Ni, Co-
Ni, Co-Ni-Fe, and the like are included, and a metal component of 20
Within the range of not more than wt%, aluminum, silicon, sulfur,
Scandium, titanium, vanadium, chromium, manganese, copper, zinc, yttrium, molybdenum, rhodium,
Palladium, gold, tin, antimony, boron, barium,
Examples thereof include alloys containing tantalum, tungsten, rhenium, gold, mercury, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, and bismuth. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide.

The method for producing these ferromagnetic powders is already known, and the ferromagnetic powder used in the present invention can also be produced according to known methods. The shape of the ferromagnetic powder is not particularly limited, but needle-shaped particles, granular particles, dice-shaped particles, rice particles, and plate-shaped particles are usually used. In particular, it is preferable to use needle-shaped ferromagnetic powder.

The above resin component, curing agent and ferromagnetic powder are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone and ethyl acetate, which are usually used in the preparation of magnetic paint, to give a magnetic paint. Kneading and dispersion can be performed according to a usual method. In addition to the above components, the magnetic paint contains α-Al ₂ O ₃ , Cr ₂
Abrasives such as O ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, silicone oils,
It may contain a commonly used additive or filler such as a dispersant. A magnetic coating material prepared from the above materials is applied onto a non-magnetic support to form a magnetic layer.

In the method for producing the magnetic recording medium of the present invention, for example, the coating solution for the magnetic layer is preferably applied to the surface of the non-magnetic support under running, and the layer thickness after drying the magnetic layer is within the range of 0.5 to 10 μm. , And more preferably 0.5 to 7.0 μm. Here, a plurality of magnetic paints may be sequentially or simultaneously applied in multiple layers. Regarding the composition, physical properties, materials, manufacturing method and the like of each layer of a magnetic recording medium having a plurality of layers such as a multilayer magnetic layer or a lower non-magnetic layer and an upper magnetic layer, JP-A-2-240824 and JP-A-2-240824 are referred. Those described in No. 21782 and the like can be used.

As a coating machine for coating the above magnetic paint,
Air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure cord, kiss coat, cast coat, spray coat, spin coat and the like can be used. For these coating methods, "coating engineering" (Asakura Shoten (1972)) or "advancement of coating technology" (Sogo Gijutsu Center (1988))
Year))).

A back layer (backing layer) may be provided on the surface of the non-magnetic support used in the present invention which is not coated with the magnetic coating material. Usually, the back layer is provided by applying a back layer forming coating in which a granular component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on the surface of the non-magnetic support which is not coated with the magnetic coating. It is a layer. An adhesive layer may be provided on the surface of the non-magnetic support on which the magnetic paint and the back layer forming paint are applied.

The applied coating layer of the magnetic coating material is dried after the ferromagnetic powder contained in the coating layer of the magnetic coating material is subjected to the magnetic field orientation treatment. After being dried in this way, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calendar roll or the like is used. By performing the surface smoothing treatment, the voids generated by the removal of the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer improves, so that a magnetic recording medium with high electromagnetic conversion characteristics can be obtained. it can.

The magnetic recording medium of the present invention is a surface having an extremely smooth surface with a center line average roughness of 4 nm or less (preferably in the range of 3 to 1 nm) at a cutoff value of 0.25 mm. Is preferred. As a method thereof, for example, a recording layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the calendering treatment. As calendering conditions, a calender roll is used in a temperature range of 60 to 100 ° C. and a pressure of 1
It is preferably carried out by operating under conditions in the range of 00 to 400 kg / cm ² . The laminate thus cured is then formed into the desired shape. The cutting can be performed under normal conditions using a normal cutting machine such as a slitter.

[0033]

The magnetic recording medium binder and the magnetic recording medium of the present invention are a binder for a magnetic recording medium containing a copolymer comprising a vinyl monomer and another copolymerizable component, wherein the vinyl monomer is vinylphenol or its derivative. Therefore, the magnetic layer or non-magnetic layer using the binder of the present invention has extremely large dispersibility and excellent electromagnetic conversion characteristics, and at the same time, dehydrochlorination from the resin constituting the magnetic layer or non-magnetic layer Since there is no problem, a magnetic recording medium having excellent long-term storage stability and durability can be obtained. Hereinafter, the present invention will be described in more detail by showing Examples of the present invention.

[0034]

【Example】

Examples 1-5 and Comparative Examples 1-2 Ferromagnetic alloy powder (composition: 94% Fe, 4% Zn, Ni2)
%, Hc 1500 Oe, crystallite size 20 nm) 100
Parts (parts represent parts by weight) were crushed with an open kneader for 10 minutes, then kneaded with 15 parts of the binder of Table 1 and 20 parts of methyl ethyl ketone and 30 parts of cyclohexanone for 60 minutes, and then polyurethane (manufactured by Toyobo Co., Ltd.). UR8300) 5 parts (solid content) Abrasive (alumina particle size 0.3 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Methyl ethyl ketone / toluene = 1/1 200 parts were added and dispersed by a sand mill for 120 minutes. Polyisocyanate (Coronate 3041 manufactured by Nippon Polyurethane Co., Ltd.) 3 parts (solid content) sec-butyl stearate 1 part Butoxyethyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 50 parts were added, and after stirring and mixing for 20 minutes, 1 μm A magnetic paint was prepared by filtering using a filter having an average pore size. The thickness of the obtained magnetic paint after drying is 2.5μ
The reverse roll was used to coat the surface of a support of aramid resin having a thickness of 8 μm so as to have a thickness of m.

The non-magnetic support coated with the magnetic coating is magnetically oriented with a magnet of 3000 gauss while the magnetic coating is undried, and after drying, a metal roll-metal roll-
Calendering with a combination of metal roll-metal roll-metal roll-metal roll-metal roll was performed at a speed of 10
The test was performed at 0 m / min, a linear pressure of 300 kg / cm, and a temperature of 90 ° C., and then slit into a width of 8 mm to prepare an 8 mm video tape sample.

Measurement method Electromagnetic conversion characteristics: Hi8-VTR (Son
The signal was recorded and reproduced by using y-TR: 705). The S / N ratio at this time was measured with a noise meter, and the value of Comparative Example 4 was set to 0 dB and expressed as a relative value.

Surface roughness Ra: The center line average roughness Ra was determined by an optical interference method using a digital optical profilometer (manufactured by WYKO) under the condition of a cutoff of 0.25 mm.

Repeatability: 0 ° C. 10% RH, 0 ° C.
A 90-minute long tape is set to 100 by using a VTR under each environment of 70% RH, 40 ° C. 10% RH, and 40 ° C. 70% RH.
After continuous running, the video head was observed for dirt, and the video output was continuously recorded to measure the decrease in output.

Dirt on the video head ○: No dirt was observed △: Observed when the dirt was wiped off ×: Observed dirt visually High temperature Repeatability after storage at high humidity: 23 ° C 30 after tape sample was exposed to 60 ° C 90% RH environment for 2 weeks
Repeatability was evaluated in the same manner as in the environment of% RH.

[0040]

[Table 1]

Examples 6 to 13 and Comparative Example 3 An undercoating liquid prepared by stirring with a Dispa stirrer for 12 hours was prepared according to the following formulation.

Polyester resin (containing —SO ₃ Na group) 100 parts by weight Tg 65 ° C. Na content 4600 ppm cyclohexanone 9900 parts by weight Using the obtained undercoat liquid, polyethylene terephthalate (thickness 10 μm, F5 value: MD direction 20 Kg / m
m ² , TD direction 14 Kg / mm ² , Young's modulus: MD direction 750 Kg / mm ² , TD direction 470 Kg / m
m ² ), and a dry thickness of 0.1 μm was applied on the non-magnetic support composed of m ² ).

On the other hand, a coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared by the following formulations. Formulation of coating liquid for upper magnetic layer Ferromagnetic powder: Fe alloy powder (Fe-Co-Ni) 100 parts by weight Composition; Fe: Co: Ni = 92: 6: 2 Al ₂ O ₃ is used as a sintering inhibitor Hc 1600 Oe , Σ _s 119 emu / g major axis length 0.13 μm, acicular ratio 7 crystallite size 17.2 nm, water content 0.6 wt% binder in Table 2 13 parts by weight polyurethane resin (UR8300 manufactured by Toyobo Co., Ltd.) 5 parts by weight α-alumina (average particle size 0.15 μm) 12 parts by weight S _BET 8.7 m ² / g, pH 8.2, water content 0.06% by weight cyclohexanone 150 parts by weight methyl ethyl ketone 150 parts by weight The above composition is sand milled. After mixing and dispersing in the inside for 6 hours,
Polyisocyanate (Coronate L) and oleic acid 5
Parts by weight, 7 parts by weight of stearic acid, 1 part of butyl stearate
5 parts by weight was added to obtain a coating liquid for the upper magnetic layer.

Coating liquid formulation for lower magnetic layer TiO ₂ 85 parts by weight Average particle diameter 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment layer Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 4. 1 pH 6.5-8.0 Carbon black 5 parts by weight Average particle size 160 nm DBP oil absorption 80 ml / 100 g pH 8.0 S _BET 250 m ² / g Coloring power 143% Binder of Table 2 13 parts by weight Polyurethane resin (Toyo Spinning Co., Ltd. UR8300) 5 parts by weight Cyclohexane 100 parts by weight Methyl ethyl ketone 100 parts by weight After mixing and dispersing the above composition in a sand mill for 4 hours,
5 parts by weight of polyisocyanate (Coronate L), 5 parts by weight of oleic acid, 5 parts by weight of stearic acid and 15 parts by weight of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

The above coating solution was applied in a wet state by using two doctors having different gaps, and after orientation treatment with a permanent magnet of 3500 gauss and then with an electromagnet of 1600 gauss, it was dried. Then, a metal roll and a super calender treatment with the metal roll were performed at a temperature of 80 ° C.
The coating thickness was 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer. Next, a coating solution for the back coat layer was prepared according to the following formulation.

Backcoat layer formulation Carbon black 100 parts by weight S _BET 220 m ² / g Average particle size 170 nm DBP oil absorption 75 ml / 100 g Volatile content 1.5% pH 8.0 Bulk density 240.2 kg / m ³ Binding of Table 2 Agent 100 parts by weight Polyurethane (Toyobo Co., Ltd. UR8300) 30 parts by weight Dispersant Copper oleate 10 parts by weight Copper phthalocyanine 10 parts by weight Barium sulfate (precipitating) 5 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight The above composition Preliminary kneading and kneading with a roll mill, based on 100 parts by weight of the obtained composition, carbon black 100 parts by weight S _BET 200 m ² / g average particle size 0.2 μm DBP oil absorption 36 ml / 100 g pH 8.5 α- Al ₂ O ₃ (average particle size 0.2 μm) 0.1 parts by weight was added to the composition of the sun. Disperse with a dog grinder,
After filtration, the following composition was added to 100 parts by weight of the above composition to prepare a coating liquid. Methyl ethyl ketone 120 parts by weight Polyisocyanate 5 parts by weight The obtained coating liquid was applied on the side of the non-magnetic support opposite to the side on which the magnetic layer was provided to a dry thickness of 0.5 μm. The raw material thus obtained is cut into a width of 8 mm to prepare an 8 mm video tape, and the result measured by the same method as in Example 1 is shown in Table 2.

[0047]

[Table 2]

Examples 14 to 4 and Comparative Example 4 A coating liquid for the upper magnetic layer and a coating liquid for the lower magnetic layer having the following compositions were prepared. Upper layer liquid CO-γ-FeOx 100 parts by weight (x = 1.45, major axis length 0.20 μm, Hc950Oe, Br1600 gauss) Binder of Table 3 10 parts by weight Polyurethane (Toyobo Co., Ltd. UR8300) 5 parts by weight Poly Isocyanate (Coronate L) 6 parts by weight Stearic acid (industrial) 1 part by weight Butyl stearate (industrial) 1 part by weight α-alumina (particle size 0.2 μm) 10 parts by weight Conductive carbon (particle size 70 nm) 1 part by weight Parts Methyl ethyl ketone / cyclohexanone = 7/3 solvent 200 parts by weight Lower layer liquid (solution B) CO-γ-FeOx 100 parts by weight (x = 1.45, major axis length 0.25 μm, Hc850Oe, Br1400 gauss) Binder of Table 3 11 parts by weight Polyurethane (Toyobo Co., Ltd. UR8300) 4 parts by weight Polyisocyanate (Coronate L) 6 Parts by weight stearic acid (industrial) 1 part by weight butyl stearate (industrial) 1 part by weight conductive carbon (particle size 20 nm) 5 parts by weight methyl ethyl ketone / cyclohexanone = 7/3 solvent 200 parts by weight.

The coating solution was adjusted by using a kneader, sand grinder or the like, and simultaneous multilayer coating was performed. The non-magnetic support has a center line average surface roughness (Ra) of 4 nm and 14 μ.
An m-thick polyethylene terephthalate film was used. After coating, it was oriented in the longitudinal direction and dried to obtain a bulk roll. The obtained bulk roll was further calendered. Calendar roll treatment is Shore A hardness 80
Degree, 7 layers of metal rolls with Ra 0.5 nm, temperature 8
It was treated at 0 ° C. and a linear pressure of 300 kg / cm ² . After the above-mentioned calender roll treatment, a bulk thermo treatment was carried out at 60 ° C. for 24 hours to cure the magnetic layer and then slit to a 1/2 inch width to obtain a video tape. When the surface roughness of the obtained video tape was measured, all were 5 to 6 nm. Table 3 shows the results obtained by incorporating the obtained video tape in an S-VHS type cassette to prepare a video cassette tape and measuring by the same method as in Example 1.

[0050]

[Table 3]

[0051]

Since the vinylphenol copolymer or the vinylphenol derivative copolymer is used as the binder, the dispersibility and electromagnetic conversion characteristics of the ferromagnetic powder are equal to or slightly higher than those of the vinyl chloride binder. Since problems such as hydrolysis of the ester of polyurethane contained by dehydrochlorination of vinyl and reduction of molecular weight of polyvinyl chloride do not occur, running durability at high temperature and durability after storage at high temperature and high humidity are vinyl chloride type. Which far exceeds the binders of. In addition, the binder of the present invention has high dispersibility, improves roll fouling in the calendar step, improves squareness and surface roughness,
As a result, the electromagnetic conversion characteristics were improved.

Claims (3)

[Claims] 1. A binder for a magnetic recording medium comprising a copolymer of a vinyl monomer and another copolymerizable component, wherein the vinyl monomer is vinylphenol or a derivative thereof. Agent. 2. A magnetic recording medium provided with a magnetic layer in which ferromagnetic powder is dispersed in a binder, wherein the binder comprises a vinyl monomer, which is vinylphenol or its derivative, and another copolymerizable component. A magnetic recording medium comprising a copolymer. 3. A magnetic recording medium in which a lower magnetic layer or a lower nonmagnetic layer is provided on at least one surface of a nonmagnetic support, and an upper magnetic layer is provided thereon, at least the magnetic layer or the nonmagnetic layer. One layer is a magnetic recording medium characterized in that the binder for dispersing the ferromagnetic powder or the non-magnetic powder contains a copolymer of vinyl phenol or a vinyl monomer which is a derivative thereof and another copolymerizable component.