JPS6216233A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has good dispersibility, lessens the decrease of a satd. magnetic flux density and surface roughness and has an excellent electromagnetic conversion characteristic by incorporating carbon black having <=0.05% ash content into a coating type magnetic recording layer provided on a non-magnetic substrate. CONSTITUTION:The carbon black having <=0.05% ash content, 20-350m<2>/g specific surface area, <=200ml/100g oil absorption and 13-60mum average grain size is incorporated into the magnetic recording layer provided on the non- magnetic substrate. The amt. of the impurities incorporated into the ash is decreased by decreasing the ash content in the carbon black, by which the dispersibility of the carbon black is improved and the decrease of the satd. magnetic flud density and surface roughness is lessened. The magnetic recording medium having the excellent electromagnetic conversion characteristic is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a coated magnetic recording layer, and particularly to a magnetic recording medium having a characteristic composition of the magnetic recording layer.

At present, magnetic recording media are widely used in the fields of audio, video, computers, magnetic disks, 8m/m, etc., and in the future, video floppies, high-density It is expected that it will be used in fields such as floppy disks, and as a result, the amount of information recorded on magnetic recording media will continue to increase year by year, and as a result, magnetic recording media will increasingly be required to have higher recording densities. It is becoming.

Conventionally, in magnetic recording media such as magnetic tape.

Magnetic properties are improved by orienting the acicular magnetic powder in the magnetic recording layer in the longitudinal direction, but those with the acicular magnetic powder oriented in the longitudinal direction can obtain high output in the low frequency band. On the other hand, high-density recording had its limitations.

Furthermore, recently, a magnetic recording medium has been proposed in which the magnetic powder is flat and uses barium ferrite magnetic powder in the magnetic recording layer, which has an axis of easy magnetization in the perpendicular direction (
JP-A-57-195328).

In particular, barium ferrite itself has an electrical resistance of 100/cm.
If a conductive substance such as carbon black is not used in combination with barium ferrite, the magnetic recording medium may stick to the head, cause dropouts, or may be damaged during the manufacturing process such as the coating process. Sticking occurs on guide rollers, calendar rollers, etc., and in severe cases, discharge noise is generated, so it is usually considered to use a conductive substance in combination, and carbon black is added to lower the electrical resistance. is normal.

However, since ordinary carbon black has poor dispersibility, gloss and saturation magnetic flux density are greatly reduced, and therefore, the influence of carbon black on electromagnetic conversion characteristics cannot be ignored. Therefore, it has been desired to improve the dispersibility, and along with this, there has been a strong desire to improve the saturation magnetic flux density and gloss.

1. Means for Solving the Problems The inventors of the present invention conducted further research to improve the above-mentioned problems, and found that the above-mentioned problems could be solved by using carbon black having specific physical properties. , the present invention has been achieved.

That is, the present invention provides a magnetic recording medium in which a coated magnetic recording layer is provided on a nonmagnetic base material, in which the magnetic recording layer has an ash content of 0.0.
The present invention relates to a magnetic recording medium characterized by containing 5% or less of carbon black.

Typically, the carbon black used in the magnetic recording layer has an ash content of at least 0.01%, as much as approximately 1%, and usually 0.3-0.4%.

Impurities that are ash are Fe2O3, Fe2 (SO4)
3. TiO2, MnO, Ca SO4, MgSO4, A
I203, SiO2, SO4, etc., and these are mixed during the production of carbon black.

It has been found that reducing these impurities improves the dispersibility of carbon black. These impurities are 0.0
When the content was less than 5%, the dispersibility improved significantly and the gloss of the magnetic recording layer increased. Therefore, it was discovered that carbon black can be used within a wider range of specific surface area, oil absorption, and average particle size.

Normally, desirable properties cannot be obtained unless the carbon black has a very limited specific surface area, oil absorption amount, and average particle size, but in the present invention, by reducing the ash content as described above, the above-mentioned wide range of carbon blacks can be obtained. It can be used.

The carbon black used in the magnetic recording layer of the present invention may be manufactured by any method such as furnace, channel, acetylene, thermal, lamp, etc.1, acetylene black, furnace black, channel black, roller and disk black, German naphthalene black is preferred. The carbon black used in the present invention has an ash content of 0.05% or less, a specific surface area of 20 to 350 m2/g, and an oil absorption amount of 200 ml/100.
Pg or less and an average particle size of 13 to 60 mP are preferred. These products are manufactured by, for example, reducing the amount of impurities in the raw material system, using special manufacturing equipment to prevent impurities from entering the manufacturing process, making cleaning extremely easy, and washing with water afterwards.

When the specific surface area and oil absorption amount are within the above ranges, it is more preferable in terms of dispersibility.

Furthermore, if the particle size exceeds 60 mP, the dispersibility will decrease, which is not preferable in terms of shape retention. On the other hand, if the particle size was less than 10 m<7>, the magnetic recording layer would not be uniformly dispersed in the paint, resulting in a decrease in surface roughness and poor shape retention.

On the other hand, the magnetic layer of the present invention can be applied to a coating type consisting of a coating film containing ferromagnetic fine particles and a binder. 'Fe2 o3. Fe304, CO doped-Fe203. Co-doped 2r -F e203-
Fe304 solid solution, Co-based compound coated type 21”-F
e203. Co-based compound coated type 21”-F e 3
04 (CO-based compounds here include intermediate oxidation states with 7Fe2O3, and include cobalt oxide, cobalt hydroxide, cobalt ferrite, cobalt ion adsorbates, etc., when the magnetic anisotropy of cobalt is utilized to improve coercive force. ), or iron, cobalt, nickel and other ferromagnetic metals, or Fe-C01F e -N i, Co-N
i, Fe-Rh, Fe-Cu, Fe-Au, C
o Cu, Co Au.

Go-Y, Co-La, Co-Pr, Go-Gd.

Co-3m, Go-Pt, Ni-Cu, Fe-Co-
Nd, Mn-Bi, Mn-8b, Mn-Al, Fe-
Examples include magnetic alloys such as Co-Cr and Co-Ni-Cr, and ferrite-based magnetic materials such as Ba ferrite and Sr ferrite.

The particle size of the magnetic particles is 0.1 to 1 on the long axis in the case of acicular powder, -
m, minor axis 0.02-0.1. &-m, in the case of granules, the average particle size is 0.01 to 0.5. It is mm.

The barium ferrite magnetic powder used in the present invention has a hexagonal plate shape and is represented by the chemical formula Ba0.6Fe203. In addition, part of Ba and Fe in this chemical formula is Ti.
, Cr, Co, Zn, In.

Also included are those substituted with metals such as Mn, Cu, Ge, Nb, Ca, Sr, Pb, and Ni.

The barium ferrite magnetic powder has a diameter of 0.2 pm or less, preferably 0.15 pm or less. −m or less, more preferably Q, IP
m or less, and the plate ratio is 6 or more, more preferably 8 or more.

In this case, the upper limit of the plate ratio is not particularly limited, but is usually 30 or less. Here, the average particle size refers to electron micrographs [scanning microscope (SEM) and transmission microscope (T
For example, about 50 cross sections of hexagonal barium ferrite particles were subjected to Ti4 deposition using EM), and the measured values for each particle size were averaged. The average thickness is also the average of the values measured by electron micrographs. In addition, the plate ratio is the average particle size/
This is the average thickness value. Alternatively, the average thickness can also be measured by the half width of X-ray diffraction. Since barium ferrite has a hexagonal plate shape, it has a greater influence on surface roughness than needle-like magnetic powder, and when the diameter and plate ratio are larger than the above, the surface roughness decreases significantly, which is not preferable. When the particle size is within the above range, the perpendicular component is fully utilized, the surface smoothness of the magnetic layer is good, the noise is sufficiently low, and high-density recording can be achieved.

Methods for producing barium ferrite include a ceramic method, a coprecipitation-firing method, a hydrothermal synthesis method, a flux method, a glass crystallization method, an alkoxide method, a plasma jet method, etc., and it goes without saying that any of these methods can be used.

Conventionally, ferromagnetic powders include, for example, 7Fe203 and CO-containing powders. -Fe203, Fe3O4, Co'-containing Fe
304. CrO2 and the like were often used, but the magnetic properties of these ferromagnetic powders, such as coercive force and maximum residual magnetic flux density, were insufficient for high-sensitivity, high-density recording, and the
, w m or less, or for magnetic recording with a narrow track width.

As requirements for magnetic recording media become more stringent, ferromagnetic powders with properties suitable for high-density recording have been developed and proposed. Such magnetic powders include Fe, Co,
Metals or alloys such as Fe-Co, Fe-Co-Ni, Co-Ni, and A1. There are alloys with Cr, Si, etc. A magnetic recording layer using such an alloy powder must have a high coercive force and a high residual magnetic flux density for the purpose of high-density recording, and various manufacturing methods or alloys are used to make the magnetic powder meet these standards. Preferably, the composition is selected.

The inventors manufactured magnetic recording media using various alloy powders, and the specific surface area measured by the BET method was 48 m2/g.
In the above, the coercive force of the magnetic layer is 10,000e or more, and the surface roughness of the magnetic layer [cutoff 0° 17 mm TR20 (average value of 20 times) measured by Talystep described later, the same applies hereinafter] is 0. 08. −When:
A magnetic recording medium having a sufficiently low noise level and suitable for high-density, short-wavelength recording can be obtained.

Organic binders, inorganic pigments, lubricants, and one other dispersant commonly used in the magnetic recording layer of the present invention.

Antistatic agents and the like can be used in a conventional manner.

The organic binder used in the magnetic recording layer of the present invention has conventionally been
Thermoplastic, thermosetting, or reactive resins used for magnetic recording media, or mixtures thereof, are used, but hardening types are used in terms of the strength of the resulting coating film.

In particular, radiation-curable resins are preferred.

As a thermoplastic resin, the softening temperature is 150°C or less, the average molecular weight is to, ooo ~ 200,000, and the degree of polymerization is about 20.
0 to 2,000, such as vinyl chloride-vinyl acetate copolymers (including those with carboxylic acid introduced),
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
(including those with carboxylic acid introduced), vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene Copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride , vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer,
1 Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate, cellulose diacetate, cellulose triacetate).

Cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. .

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferable, such as phenol resins, epoxy resins, polyurethane curable resins, urea resins, and melamine resins.

Alkyd resin, silicone resin, acrylic reactive resin,
Epoxy-polyamide resins, nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycol/ High molecular weight diol/triphenylmethane triisocyanate mixtures, polyamine resins, and mixtures thereof.

It is preferable to use a hardened radiation-curable compound as the binder.

A specific example of the radiation-curable compound is acrylic acid, which has an unsaturated double bond that exhibits radical polymerization.

Crosslinking or polymerization drying by radiation irradiation of acrylic double bonds such as methacrylic acid 5 or their ester compounds, allylic double bonds such as diallyl phthalate, unsaturated bonds such as maleic acid and maleic acid derivatives, etc. This is a resin in which a group is contained or introduced into the molecule of a thermoplastic resin. Any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used.

The following unsaturated polyester resins are examples of thermoplastic resins containing groups in their molecules that can be crosslinked or polymerized and dried by radiation irradiation.

A polyester compound containing a radiation-curable unsaturated double bond in its molecular chain, for example, a saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol as shown in (2) below, in which part of the polybasic acid is replaced by maleic acid. Examples include unsaturated polyester resins containing radiation-curable unsaturated double bonds.

Radiation curable unsaturated polyester resin contains polybasic acid component 1
Maleic acid, fumaric acid, etc. are added to one or more seeds and one or more polyhydric alcohol components, and the mixture is heated to 180
~200℃, under nitrogen atmosphere, after dehydration or dealcoholization reaction, increase temperature to 240~280℃, 0.5~1m
It can be obtained by a condensation reaction under reduced pressure of mHH. The content of maleic acid, fumaric acid, etc. in the acid component is 1 to 40 mol%, preferably 1
It is 0 to 30 mol%.

Examples of thermoplastic resins that can be modified into radiation-curable resins include the following.

(1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, such as VROH, VYNC, VYBGX, VERR, VYE manufactured by UCC
Examples include S, VMCA, VA, GH, etc., and radiation sensitivity modification is carried out by introducing an acrylic double bond, a maleic acid double bond, or an allylic double bond into this material by the method described below.

(2) Saturated polyester resin Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1°2 propylene glycol,
1.3 Butanediol, dipropylene glycol, 1,
4 butanediol, 1.6 hexanediol, pentaerythritol.

Sorbitol, glycerin, neopentyl glycol,
Examples include saturated polyester resins obtained by ester bonding with polyhydric alcohols such as l,4-cyclohexane dimetatool, or resins obtained by modifying these polyester resins with SO3Na etc. (e.g. Vylon 53S), and these can also be treated in the same manner. Radiation sensitivity degeneration is performed.

(3) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components, and the hydroxyl groups contained in these resins are subjected to radiation-sensitive modification by the method described below.

(4) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methylepichlorohydrin.

For example, Shell Chemical (Epicoat 152.154.82)
8.1001.1004.1007), manufactured by Dow Chemical (DEN431, DE R732, DER511, D
ER331), manufactured by Dainippon Ink (Epicron 400,
800), and furthermore, UC which is a high polymerization degree resin of the above epoxy
Phenoxy resin manufactured by Company C (PKHA, PKHC, PKHH
), copolymer of brominated bisphenol A and epichlorohydrin, Dainippon Ink Chemicals 1ll (Epiclon 1
45, 152, 153, 1120), and these also include those containing a carboxylic acid group. Radiation sensitivity modification is performed using the epoxy groups contained in these resins.

(5) Various types of Mll fibrin derivatives are used, but particularly effective ones include nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, acetyl cellulose, etc.
Radiation sensitivity modification is performed using the hydroxyl groups in the resin by the method described below.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, Acrylic resins containing at least one type of acrylic ester and methacrylic ester containing hydroxyl groups as a polymerization component are also effective.

Examples of elastomers or prepolymers are listed below.

(1) The use of polyurethane elastomers or prepolymer polyurethanes is particularly effective in terms of their abrasion resistance and good adhesion to substrate films, such as PET films. Examples of urethane compounds include isocyanates such as 2.4-)-toluene diisocyanate, 2.6-toluene diisocyanate, 1.3-xylene diisocyanate, 1,4-xylene diisocyanate, and 1.5-
Naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'
-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate,
3,3'-dimethylbiphenylene diisocyanate, 4
, 4'-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,
Various polyvalent isocyanates such as dicyclohexylmethane diisocyanate, Desmodur and Desmodur N, and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol, 1,6-hexanediol, penta Polyhydric alcohols such as erythritol, sorbyl, neopentyl glycol, 1,4-cyclohexane dimetatool and saturated polyhydric alcohols such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid. Polycondensation products of various polyesters such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic esters, hydroxyl-containing methacrylic esters, etc. Polyurethane elastomers and prepolymers consisting of are effective.

1 It is very effective to modify these urethane elastomers to make them radiation sensitive by reacting their terminal isocyanate groups or hydroxyl groups with monomers having acrylic double bonds or allylic double bonds. It is. It also includes those containing ○H, COOH, etc. as a polar group at the terminal.

Furthermore, monomers having an unsaturated double bond having active hydrogen that reacts with an incyanate group and having radiation curability, such as mono- or diglycerides of long-chain fatty acids having an unsaturated double bond, are also included.

(2) Acrylonitrile-butadiene copolymer elastomer Elastomers such as an acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD Retired Resin manufactured by Sinclair Petrochemical Co., Ltd. or Hiker 1432 J manufactured by Nippon Zeon Co., Ltd. are particularly suitable for use in butadiene. It is suitable as an elastomer component whose double bond generates radicals by radiation and is crosslinked and polymerized.

(3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Retired Resin R-15 manufactured by Sinclair Petrochemical Co., is particularly suitable in terms of compatibility with thermoplastic resins. R
Since the -15 prepolymer has a hydroxyl group at the molecular end, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the molecular end, making it more advantageous as a binder.

In addition, polybutadiene cyclized product, CBR- manufactured by Japan Synthetic Rubber Co., Ltd.
M901 also has excellent properties when combined with thermoplastic resin.

Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber,
Chlorinated rubber, acrylic rubber, isoprene rubber, and their cyclized products (Japan Synthetic Rubber iJc I R701) are available, and elastomers such as epoxy-modified rubber and internally plasticized saturated linear polyester (Toyobo Vylon 3300) can also be treated with the radiation-sensitive modification treatment described below. It can be used effectively by applying

Compounds having radiation-curable unsaturated double bonds used as oligomers and monomers in the present invention include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1,6- Hexane glycol diacrylate, 1,6-hexane glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, polyfunctional oligoester acrylate (Aroex M-7100, M-
5400, 5500, 5700, etc., Toagosei), acrylic modified products of Tuboran 4040) in urethane elastomers, or those into which functional groups such as C0OH have been introduced, trimethylolpropane diacrylate (methacrylate), phenol ethylene oxide Adduct acrylate (methacrylate), a compound with an acrylic group (methacrylic group) or ε-caprolactone acrylic group attached to a pentaerythritol condensed ring represented by the following general formula.

In the formula, m=1. a=2. Compound b"4 (hereinafter referred to as "compound")

special pentaerythritol condensate A), m=1,
a=3. A compound where b=3 (hereinafter referred to as special pentaerythritol condensate B), m=1, a=6. Compound where b=o (hereinafter referred to as special pentaerythritol condensate C)
, m=2, a=6. Examples include compounds where b=o (hereinafter referred to as special pentaerythritol condensates), and special acrylates represented by the following general formula.

(1) (CH2=CHCOOCH2) 3-CCH20
H (special acrylate A) (2) (CN2= CHCOOCH,) 3 CC
HzCH3 (special acrylate B) (3) [CN2= CHCO-+OC3H,4)n
-0CII) 3- CCII, CH3 (n=3)
(Special acrylate C) (Special acrylate D
) (Special acrylate F) (n”; 16) CHC00C)I
= GHz (special acrylate G) (8) CHJ7Ct (Coo (CN2 Hz)
O) 4 COC11=CH2 (special acrylate H
) (Special acrylate ■) CR, CI, O- and 0- (CH, ), -0COCH=
C) l 2 (Special Acrylate J) A Niacrylic Acid, X: Polyhydric Alcohol Y: Polybasic Acid (Special Acrylate K) Next, an example of the synthesis of the radiation-sensitive binder will be described.

a) Synthesis of Agril modified product (radiation sensitive modified resin) of vinyl chloride vinyl acetate copolymer resin Partially saponified vinyl chloride vinyl acetate copolymer having CH groups (average degree of polymerization n = = 500
) 750 parts, toluene 1250 parts, cyclohexanone 5
Pour 00 parts into 4 flasks of No. 51 and heat and dissolve.
After raising the temperature to 0°C, 61.4 parts of 2-hydroxyethyl methacrylate adduct × of tolylene diisocyanate was added,
Furthermore, 0.012 parts of tin octylate and 0.0 parts of hydroquinone.
012 parts was added and the NGO reaction rate was 9 at 80°C in a N2 stream.
Allow to react until it reaches 0%. After the reaction is completed, the mixture is cooled and diluted with 1250 parts of methyl ethyl ketone.

(×Production of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) 348 parts of TDI was heated to 80°C in a 11-hole flask in a N2 stream, then 260 parts of 2-ethylene methacrylate and 0 tin octylate were added. .07 parts, hydroquinone 0.05
After completion of the dropwise addition, the mixture was stirred at 80°C for 3 hours to complete the reaction while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85°C. After the reaction was completed, the reactor was taken out and cooled to obtain TDI 2HEMA in the form of a white paste. b) Synthesis of acrylic modified butyral resin (radiation-sensitive modified resin) 100 parts of butyral resin Seed Water Chemical IIBM-8 was mixed with 191.2 parts of toluene and 4 parts of cyclohexanone 71°.
Four parts of 1 were placed in a flask, heated and dissolved, and after raising the temperature to 80°C, 7.4 parts of TDI's 2HEMA Adduct
The reaction rate of NC○ in N2 gas stream was 90% at 80"C.
Let it react until it reaches the above level. After the reaction is completed, the mixture is cooled and diluted with methyl ethyl ketone.

C) Synthesis of acrylic modified saturated polyester resin (radiation-sensitive modified resin) Saturated polyester resin (Vylon RV-200 manufactured by Toyobo Co., Ltd.)
), 100 parts of TDI was dissolved in 116 parts of toluene and 116 parts of methyl ethyl ketone and heated to 80°C.
Add 3.555 parts of Adduct x, 0.007 part of tin octylate, and 0.007 part of hydroquinone, and react at 80°C in a N2 stream until the NC○ reaction rate reaches 90% or more.

d) @Synthesis of acrylic modified epoxy resin (radiation-sensitive modified resin) Epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.), 4
After heating and dissolving 00 parts in toluene 50 parts and methyl ethyl ketone 50 parts, N,N-dimethylbenzylamine 0.00
6 parts of hydroquinone and 0.003 parts of hydroquinone were added, the temperature was raised to 80°C, 69 parts of acrylic acid was added dropwise, and the mixture was allowed to react at 80°C until the acid value reached 5 or less.

◎Synthesis of acrylic modified phenoxy resin (radiation-sensitive modified resin) ○600 parts of phenoxy resin having H group (manufactured by PKHHCUCC, molecular weight 30.000) and 1800 parts of methyl ethyl ketone were placed in a 31-4 solo flask, heated and dissolved, and After raising the temperature to ℃, 6.0 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate was added,
Furthermore, 0.012 parts of tin octylate and 0.0 parts of hydroquinone.
012 parts of the mixture were added and allowed to react at 80°C in a N2 stream until the NGO reaction rate reached 90%. The molecular weight of this phenoxy modified product is 35,000. There is one double bond per molecule.

e) Synthesis of acrylic modified urethane elastomer (radiation-curable elastomer) 250 parts of a diphenylmethane diisocyanate (MDI)-based urethane prepolymer having a terminal isocyanate (Nipporan 3119 manufactured by Nippon Polyurethane), 2HEMA32.
5 parts, hydroquinone 0.07 parts, tin octylate Q,
Pour 009 parts into a reaction can and heat to 80°C to dissolve TDT4.
3.5 parts were added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and the reaction rate was 9 at 80°C after the completion of dropping.
The reaction is allowed to occur until the concentration reaches 5% or more.

f) Synthesis of acrylic modified polyether-terminated urethane-modified elastomer (radiation-curable elastomer) Polyether PTG-500, 2 manufactured by Nippon Polyurethane Co., Ltd.
50 parts, 2HEMA 32.5 parts, hydroquinone 0.0
07 parts and 0.009 parts of tin octylate were placed in a reaction can.
After heating and dissolving at 80°C, 43.5 parts of TDI was added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and after the dropwise addition was completed, the reaction was allowed to occur at 80°C until the reaction rate reached 95% or more.

g) Synthesis of acrylic modified polybutadiene elastomer (radiation curable elastomer) Low molecular weight terminal hydroxyl group polybutadiene polyBD Liquid Resin R-15,250 manufactured by Sinclair Petrochemical Co., Ltd.
part, 2HEMA32.5 parts, hydroquinone 0.007 parts
Place 0.009 parts of tin octylate in a reaction vessel, and add 80 parts of tin octylate.
After heating and dissolving 43.5 parts of TDI at ℃, the temperature inside the reaction vessel was 8.
The mixture is added dropwise while cooling to 0 to 90°C, and after the dropwise addition is completed, the reaction is allowed to proceed at 80°C until the reaction rate reaches 95% or more.

It is known that some polymers disintegrate when irradiated with radiation, while others cause crosslinking between molecules. Examples of substances that cause crosslinking between molecules include polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. With such crosslinked polymers, the crosslinking reaction occurs even without the above-mentioned modification, so these resins can be used as they are for radiation crosslinking in addition to the modified products described above.

Furthermore, according to this method, even solvent-free resins that do not use solvents can be cured in a short time.
Such resins can be used.

Particularly preferred are cellulose resins (nitrified cotton, etc.),
Thermosetting resin consisting of a combination of vinyl chloride-vinyl acetate-vinyl alcohol copolymer, urethane (using a curing agent), or vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including those with carboxylic acid introduced),
or acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including those with carboxylic acid introduced)
and a radiation-curable resin consisting of urethane acrylate.

The molecular weight of the polymer is determined by the number average molecular weight measured by the following method.

*Measurement of average molecular weight of binder by GPC
el Permeation Chromatog
(Raphy) is a method of separating molecules in a sample based on their size in a mobile phase, and is a method in which liquid chromatography is performed by filling a column with a porous gel that acts as a molecular sieve.

To calculate the average molecular weight, use polystyrene of known molecular weight as a standard sample and create a calibration curve from its elution time. From this, calculate the average molecular weight in terms of polystyrene.

There are molecules with molecular weight Mi in a given high molecular weight substance.
If there are i pieces, it can be expressed as number average molecular weight=ΣN i M i.

It is preferable to use a ΣN+ radiation-curable resin because the curing time is short and there is no transfer of filler, etc. after one winding. On the other hand, in the case of thermosetting resins, the difference in electromagnetic conversion characteristics between the inside and outside of the jumbo roll during thermosetting poses a problem due to back mold transition due to tightness of the roll during curing.

In addition, as a curing agent used for thermosetting resin, TDI
, MDI, IPDI, HMDI, MDI, etc., but all commonly used curing agents can be used, and incyanate-based curing agents are particularly preferred; examples thereof include Crispon 4565 manufactured by Dainippon Ink and Chemicals Co., Ltd. ．．
4560, Coronate manufactured by Japan Polyurethane Industries Co., Ltd. and Takenate XL-1 manufactured by Takeda Pharmaceutical Company Limited.
007 can be mentioned.

The magnetic layer may contain an inorganic pigment.

Examples of inorganic pigments include 1) electrically conductive carbon black and graphite, and 2) 5i02.
TiO2, Al2O3, Cr2O5iC, Cab, Ca
CO3, zinc oxide, goethite, 2rFe203. Examples include talc, kaolin, CaSO3, boron nitride, graphite fluoride, molybdenum disulfide, and ZnS. In addition, the following fine particle pigments (aerosil type, colloidal type): 5i02. , Al2O3, T i 02, ZrO2
, Cr 203 , Y203 , Ce 02 , Fe
3O4, Fe2O3, ZrSiO4, 5b205, Sn
○ etc. are also used. These fine particle pigments are, for example, 5i0
In the case of 2, ■Ultrafine particle colloidal solution of silicic anhydride (Snowtex, water-based, methanol silica sol, etc., account chemistry)
, (2) Ultrafine particle state Hosilica (standard product 10OA) (Aerosil, Nippon Aerosil Co., Ltd.) produced by combustion of purified silicon tetrachloride. Further, the ultrafine particle colloidal solution of (1) above, ultrafine aluminum oxide produced by the same vapor phase method as (2), titanium oxide, and the above-mentioned fine particle pigment may be used. The appropriate amount of such inorganic pigments to be used is 1 to 30 parts by weight per 100 parts by weight of the binder for 1), and 1 to 30 parts by weight for 2). It has the disadvantage that it becomes brittle and more likely to drop out.

Regarding the diameter of the inorganic pigment, 1) is 0.1.
mm or less, preferably 0.05 pm or less, 2)
Regarding 0.7. +-bm or less, even 0.05.
-m or less is preferable.

The magnetic layer may contain a dispersant.

Dispersants include organic titanium coupling agents, silane coupling agents, and surfactants; antistatic agents include natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol;
Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids.

Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as sulfuric acid or phosphoric esters of amino acids, aminosulfonic acids, and amino alcohols are used.

The magnetic layer may contain a lubricant.

As lubricants conventionally used in this type of magnetic recording media, silicone oil, fluorine oil, fatty acids, fatty acid esters, paraffin, liquid paraffin, surfactants, etc. can be used, but fatty acids and/or Preferably, fatty acid esters are used.

Fatty acids include caprylic acid, capric acid, lauric acid,
myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linuric acid,
Fatty acids with 12 or more carbon atoms such as stearolic acid (RC○O
H and R are alkyl groups having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms; A fatty acid ester consisting of a monobasic fatty acid having 17 or more monobasic fatty acids and a monohydric alcohol having a total of 21 to 23 carbon atoms is used, and an alkali metal or alkali of the fatty acid is used. Metal soaps made of earth metals, lecithin, etc. are used.

As the silicone, those made of fatty acid-modified silicones and those partially fluorine-modified are used. The alcohol used is one made of higher alcohol, and the fluorine used is one obtained by electrolytic substitution, telomerization, oligomerization, etc.

Among the lubricants, radiation-curable ones are also advantageously used.

Radiation-curable lubricants include compounds that have a molecular chain exhibiting lubricity and an acrylic double bond in their molecules, such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters. , methyl vinyl alcohol ester, furyl alcohol ester, glyceride, etc. These lubricants are represented by the structural formula: CH2=CH-CH2COOR1 C) I2=CHCONHCH20COR1RCOOCH
2-CH=CH2, etc., where R is a linear or branched saturated or unsaturated hydrocarbon group, and the number of carbon atoms is 7 or more, preferably 12 or more and 23 or less, and these should be fluorine-substituted. You can also do it. As a fluorine substituted product, (:, nF2n+1-1CnF2n++(CH2)++
+ (However, m=1 to 5), R CnF2n+I SO2NC82CH2-1 Preferred specific examples of these radiation-curable lubricants include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), and glycerin methacrylate (acrylate). , glycol methacrylate (acrylate), silicone methacrylate (acrylate), and the like.

A magnetic recording layer that does not contain lubricant has a high coefficient of friction, which causes image fluctuations and jitters.In addition, the high coefficient of friction, especially when running at high temperatures, tends to cause the magnetic recording layer to be scraped, causing curling. This is likely to occur. In addition, disk media may have poor running durability or scratches on the coating film.

Dispersants include organic titanium coupling agents, silane coupling agents, and surfactants; antistatic agents include natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol;
Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphoniums or sulfoniums; Contains acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups Anionic surfactants; amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used.

Antistatic agents include conductive fine powder such as carbon black; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts, and pyridine. Cationic surfactants such as other heterocycles, phosphoniums or sulfoniums; anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, sulfuric ester groups, phosphoric ester groups; amino acids, aminosulfonic acids, amino alcohols Ampholytic activators such as sulfuric acid or phosphoric acid esters are used.

In the present invention, the mixing ratio of barium ferrite magnetic powder and carbon black is 0.1 to 30 wt%, preferably 2 to 20 wt% of carbon black to barium.

Also, the mixing ratio of barium ferrite magnetic powder and organic binder is barium ferrite/binder = 1/1 to 9.
/1, preferably 2/1 to 8/1.

Furthermore, the proportions of carbon black, inorganic oxide pigments, organic binders, lubricants, and other additives are as follows.
The organic binder is preferably 4/1 to 1/4. If it is too large, it will be difficult to disperse, and if it is too small, the magnetic recording layer will become brittle. More preferred is 3/1 to 1/3.

Further, the organic binder: lubricant ratio was 100:20.

If the amount of binder is too large, blocking will occur, and if the amount of binder is too small, adhesion will occur during one calendering step, which is not preferable.

The thickness of the magnetic recording layer of the present invention after coating and drying is 0.1~
10. -m range is common.

When the lubricant and organic binder of the magnetic layer are radiation-curable, the active energy ray used for crosslinking is an electron beam using a radiation accelerator as the source.

7HA using Co60 as a radiation source, β-rays using Sr90 as a radiation source, X-rays or ultraviolet rays using an X-ray generator as a radiation source, etc. are used.

In particular, as an irradiation source, it is advantageous to use radiation using a radiation heater from the viewpoints of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation.

Solvents used to mix and apply barium ferrite magnetic powder, carbon, organic binders, and other additives include, for example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methanol, ethanol, propatool, Alcohols such as butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether; glycol ethers such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene, toluene, xylene tar-based (aromatic hydrocarbons) such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, and other chlorinated hydrocarbons, as well as tetrahydropran, dimethylformamide, etc. are used.

These solvents are 10 to 10,000w to the binder.
t%, especially 100-5000wt%.

Non-magnetic substrates used in the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polyimide, polycarbonate, polysulfone, polyethylene naphthalate, aromatic aramid, aromatic polyester. , aluminum, glass, etc., but are not limited to these. Particularly preferred are polyester, polyimide, and the like.

The magnetic recording medium of the present invention can be manufactured by a conventional method. For example, a mixed dispersion of magnetic powder, binder, and other additives is applied to the surface of a non-magnetic substrate, and the orientation method can be in-plane, non-oriented, or vertically aligned.For example, in the case of vertically aligned, vertically aligned while drying. Magnetic particles are oriented perpendicularly to the surface of the non-magnetic substrate using a magnetic field.

Immediately thereafter, the binder is cured or crosslinked to obtain a desired magnetic recording medium. In addition, for the magnetic recording layer.

It is also possible to provide an undercoat layer under the magnetic layer and a topcoat layer on the magnetic layer. There is a back coat,
For disc use, both sides may be coated.

Typical orientation methods used are permanent magnets, DC magnetic fields, and AC magnetic fields.
In the case of vertical orientation, various combinations are used, such as a combination of vertical and horizontal, a combination of a permanent magnet or a DC magnetic field and an AC magnetic field, mechanical orientation, or a combination of mechanical orientation and the above.

Then, in order to prevent the magnetic particles oriented outside the magnetic field due to the demagnetizing field from being disturbed and deteriorating their orientation, they are dried in the magnetic field, and the magnetic particles are dried within the magnetic field so that they will not be affected by the demagnetizing field. It is necessary to dry it to a certain extent so that the magnetic powder does not move.

Further, the magnetic recording medium of the present invention can also be provided with a back layer, a top coat layer, and an undercoat layer.

The back layer, top coat layer, and undercoat layer are thermoplastic resins that are binders and additives such as inorganic pigments, lubricants, dispersants, and antistatic agents that are commonly used.

It is contained together with a thermosetting resin or a radiation-curable resin. The resin is of a radiation curing type, with its mold retention,
It is preferable from the viewpoint of economic efficiency and influence on dropout, etc., and the same additives as those for the magnetic recording layer are used as additives.

Lost garden M Examples of the present invention are shown below. Note that it should be understood that the present invention is not limited to this example.

The characteristics were evaluated as follows.

(1) Surface roughness R2° This was carried out according to the method for determining the 10-point average roughness specified in JISBO601. Note that although JIS specifies a 10-point average method, the evaluation method of the present invention uses a 20-point average method to make it more precise.

The cutoff value is stylus speed 30. -0 at m/secC
．． The frequency was approximately 18 to 9 Hz, or the needle pressure was 2 mg.

The stylus type surface roughness measuring device used was Talystep-1, T.
Manufactured by AYLORHOBSON.

(2) Vertical Square Ratio The vertical square ratio B r /B m of the magnetic tape was measured and demagnetically corrected.

(3) Linear recording density optical (KFRPI) rotation speed 30 Or, p, m, head; ferrite head, gap 0.3. Output in low recording density area in mm (
Linear recording density D where E) is E/2 in the high recording density area 5
-0 (KFRPI) was measured.

Several types of magnetic layers as described below were formed, magnetic tapes made of these layers were manufactured, and the effects of the present invention were observed.

Example 1 ◎Magnetic (gold-acid arsenide type member roof (thermosetting magnetic layer) Part by weight cobalt coated acicular ?Fe2O3 120 parts (major axis 0.4P, single axis O
, OS, -1He 6000 e) Carbon black 5 parts (ash content 0.01%, specific surface area 110 m2/g, oil absorption 125 ml/100
g, average particle size 27 m, -) a-AI203 powder (0,5, - powder) 2 parts dispersant (soybean oil refined lecithin) 3 parts solvent (ME
The above composition is mixed in a ball mill for 3 hours to better wet the acicular magnetic iron oxide with the dispersant.

Next, 15 parts of vinyl chloride vinyl acetate copolymer (VAGH manufactured by Union Carbide), 15 parts of thermoplastic urethane resin (Niraporan 3022 manufactured by Nippon Polyurethane), 200 parts of solvent (MEK/toluene 50150), and 200 parts of lubricant (higher fatty acid modified silicone oil) ) Mix and dissolve 3 parts of the mixture well.

This was placed in the ball mill that had been subjected to the magnetic powder treatment and dispersed again for 42 hours. After dispersion, 5 parts (in terms of solid content) of an isocyanate compound (Desmodur L manufactured by Bayer AG) capable of reacting with and crosslinking functional groups, mainly hydroxyl groups, of the binder in the magnetic paint were added to the ball milled paint for 20 minutes. Mixing was done.

15. Magnetic paint. - After coating on a polyester film, orienting it on a permanent magnet for in-plane orientation (2000 Gauss), and drying the solvent with an infrared lamp or hot air, 1
After the surface smoothing treatment, the roll was kept in an oven kept at 80° C. for 48 hours to accelerate the crosslinking reaction by isocyanate.

Table 1 shows the characteristics of the magnetic recording media described above and a comparative example using carbon black with an ash content of 01%.

Since the material of the present invention has good dispersibility, there is no decrease in saturation magnetic flux density (Bm), resulting in good orientation, output, and surface roughness.

Gender 2 Ejaculation Type H Various alloy powders were produced by wet reduction method.

These are composed of acicular particles with an axial ratio (short axis/long axis) of 115 to 1/10, residual magnetic flux density of 2000 to 3000 Gauss, coercive force of 1000 to 20000e: BET specific surface area of 45
~70m2/g. These magnetic powders were mixed in the following mixing ratio in a conventional manner to form each magnetic layer.

Part by weight Fe-Co-Ni alloy powder 100 (Hc
= 12000 e, major axis 0.4 part m, minor axis 0゜0
5 parts m, BET specific surface area 52 m27 g) Carbon black! 0 (ash content 0.05%, specific surface area 140 m2/g.

Oil absorption 100ml/100g, average particle size 30
m, -) Vinyl chloride/vinyl acetate/vinyl alcohol copolymer (
15 Acrylic double bond-introduced salt-vinyl acetate copolymer 10 (solid content equivalent) Acrylic double bond-introduced urethane 10 Methyl ethyl ketone/toluene (1/1) 250 Myristic acid 2 Sorbitan stearate 2 This magnetic paint was applied to a polyester film to a thickness of 3.5 cm, and subjected to electron beam curing and calendering.

As a comparative example, the carbon black in the magnetic layer 2 had an ash content of 0.8%, a specific surface area of 140 m2/g, and an oil absorption amount of 1.
A magnetic layer with a particle size of 00 ml/100 g, an average particle size of 27 m, and - was used (Comparative Example 2).

Table 2 shows the characteristics of both.

Table 2 Since the products of the present invention have good dispersibility, there is no decrease in saturation magnetic flux density, and therefore C-8/N is also good, and the surface roughness is also good.

3 H type Weight part barium ferrite 120 (diameter 0.IP, thickness 0
．． 01P, He 8000e) Carbon black 10 (ash content 0
．． 01%, specific surface area 110m2/g, oil absorption 125ml
/100g, average particle size 27m/-) Al2O3 powder (0.5P powder) 2 Solvent (M
EK/Toluene 50150) 100 The above composition is mixed in a ball mill for 3 hours to thoroughly wet the hexagonal plate-shaped barium ferrite.

Next, chlorine, vinegar, vinyl alcohol copolymer (containing maleic acid), molecular weight 40.000, 6 parts (solid content equivalent), acrylic double bond-introduced salt, vinyl acetate copolymer (containing maleic acid), molecular weight 20.000, 12 parts (In terms of solid content) Acrylic double bond-introduced polyether urethane elastomer Molecular weight 40.000 9 parts (In terms of solid content) Pentaerythritol triacrylate 3 parts Solvent (MEK/
)-Luene 50150) A mixture of 200 parts stearic acid, 4 parts butyl stearate, and 2 parts binder is thoroughly mixed and dissolved. This was put into the ball mill that had been subjected to the magnetic powder treatment and mixed and dispersed again for 42 hours.

The magnetic paint thus obtained was applied onto a 33P polyester film, vertically oriented while drying on a permanent magnet (3000 Gauss), and then the solvent was dried with an infrared lamp or hot air, and the surface was smoothed. After processing, E
Using an electrocurtain type electron beam accelerator manufactured by SI, the coating film was cured by irradiating electron beams in an N2 atmosphere under conditions of an acceleration voltage of 150 KeV, an electrode current of 20 mA, and a total irradiation dose of 5 Mra'd. .

When the plate ratio of the hexagonal plate barium ferrite in the magnetic layer 3 is changed, the degree of vertical orientation changes as shown in FIG.

If the plate-like ratio is less than 6, the degree of vertical alignment is poor, and if it is 6 or more, the plate-like ratio becomes large, making it easy to vertically align.

In addition, as shown in Table 3, the particle size is 0. A particle size of Ipm or less is recommended for mold retention, but a particle size of 0.2P is acceptable for practical use.
Can be used up to m. Particularly preferred is 0.15
．． - up to m.

Table 3 The above particle size is 0.10. - characteristics are shown in Table 4.

Carbon black with an ash content of 0.1% was used as a comparative example.

Table 4 1 average grade (thermosetting magnetic layer) Part by weight Barium ferrite magnetic powder 120 (diameter 0.IP,
Thickness 0.015P-He 10000 e) Carbon black 1° (ash content 0.03%,
Specific surface area 120m2/g, oil absorption 110ml/100g
, average particle size 2゜m) -) 1 Al2O3 powder (o, 5P powder) 2 Dispersant (
Soybean oil refined lecithin) 3 solvents (MEK/
The above composition is mixed in a ball mill for 3 hours to better wet the hexagonal platelet barium ferrite with the dispersant. Next, vinyl chloride vinyl acetate copolymer 15 (VAGH manufactured by Union Carbide), thermoplastic urethane resin 15 (Nilaporan 3022 manufactured by Nippon Polyurethane), solvent (MEK/
A mixture of 200 parts of toluene (50150) and 3 parts of a lubricant (higher fatty acid modified silicone oil) was thoroughly mixed and dissolved.

This was placed in the ball mill that had been subjected to the magnetic powder treatment and dispersed again for 42 hours. After dispersion, 5 parts (in terms of solid content) of an isocyanate compound (Desmodur L manufactured by Bayer AG) capable of reacting with and crosslinking functional groups, mainly hydroxyl groups, of the binder in the magnetic paint were added to the ball milled paint for 20 minutes. Mixing was done.

Apply magnetic paint on 73P polyester film,
After vertical orientation while drying on an alternating current magnetic field (3000 gauss) and drying of the solvent with an infrared lamp or hot air, after surface smoothing treatment, the roll was kept in an oven maintained at 80 °C for 48 hours, and the roll was heated with isocyanate. Accelerated crosslinking reaction.

The outside and inside in the examples in Table 5 indicate the outside and inside of the jumbo roll, respectively.

D50 represents the linear recording density characteristic in a high density region where the low frequency output (E, ) falls to half.

There was some tightness inside the jumbo roll, and the recording density was slightly lower with heat curing.

By suppressing the ash content of the carbon black, the dispersibility becomes good, there is no decrease in saturation magnetic flux density and surface roughness, and the electromagnetic conversion characteristics are excellent. Therefore, audio,
In terms of video and digital characteristics, it has excellent linear recording density characteristics6.Moreover, even if the ash content of carbon black is suppressed1, it has the same electrical resistance as ordinary carbon. As a result, dropouts and error rates can be suppressed, and it is also possible to take measures against sharpness and distortion noise during the process.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the plate ratio and the degree of vertical orientation of barium ferrite.

Claims (3)

[Claims] (1) A magnetic recording medium comprising a coated magnetic recording layer provided on a non-magnetic base material, wherein the magnetic recording layer contains carbon black with an ash content of 0.05% or less. (2) Carbon black with ash content of 0.05% or less has a specific surface area of 20 to 350 m^2/g and oil absorption of 200 ml/100
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has an average particle diameter of 10 to 60 mμ. (3) The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording layer contains barium ferrite magnetic powder.