JP2001155324A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in electromagnetic conversion characteristic and travelling durability. SOLUTION: This magnetic recording medium is constituted so that an under layer containing nonmagnetic or ferromagnetic powder and a binder is formed on a nonmagnetic support and at least one magnetic layer in which ferromagnetic powder and a binder are dispersed is formed on the under layer. The ferromagnetic powder contains Fe as a principal component, 10-40 atomic % Co, 2-20 atomic % Al and 1-15 atomic % Y and the organic phosphorus compound shown by the formula: [(R)m-ϕ-O]n-P(=O)(OH)3-n (wherein R is an optionally substituted alkyl, aryl or aralkyl group; m is 1-5; n is 1 or 2) is incorporated at least in the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for preparing a magnetic layer comprising a ferromagnetic fine powder dispersed in a binder on at least one side of a non-magnetic support, or a method for dispersing a non-magnetic powder in a binder. The present invention relates to a magnetic recording medium provided with a dispersed non-magnetic coating layer on a non-magnetic support and further provided with a magnetic layer and having extremely excellent electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art As a magnetic recording medium for audio, video, computer and the like, a magnetic recording medium having a magnetic layer in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support has been used. I have. In recent years, even in the field of home video tape recorders, the practical use of digital recording with less deterioration of recording has been progressing from conventional analog recording, but generally more signals are recorded in digital recording than in analog recording. In addition, the recording / reproducing apparatus and the recording medium to be used are required to have high image quality and high sound quality, and at the same time, to be downsized and space-saving. In order to achieve high-density recording, it is necessary to shorten the wavelength of the recording signal and narrow the track of the recording locus, which requires finer ferromagnetic powder, higher filling, ultra-smoothing of the medium surface, etc. At the same time, the writing speed and reading speed of the recording medium need to be reduced, and the number of rotations of the cylinder and the transport speed of the magnetic tape have been improved.

In a device using a magnetic recording medium, there is a problem that the magnetic head is stained because the medium and the magnetic head are in sliding contact with each other. In particular, in a device for high-density recording, the rotation speed of a magnetic head is increasing, and in a digital video tape recorder, the rotation speed of a magnetic head is 9600 rotations / minute, which is one of the home-use analog video tape recorders.
The rotation speed is much higher than 800 rotations / minute and 5000 rotations / minute for business use. The sliding speed between the magnetic recording medium and the magnetic head increases, and small magnetic heads such as thin-film heads are used. ing. Therefore, while the tape is running repeatedly, dirt adheres to the magnetic head and the reproduction output decreases, causing an increase in errors due to dropout, and significantly reducing the reliability of data recording and reproduction. Happens.

[0004] In order to solve such a problem, ferromagnetic metal powder is highly dispersed in a binder so that magnetic recording can be performed stably even in high-density recording and reproduction. In order to provide a medium, it has been proposed to use a dispersant such as an organic phosphorus compound in a magnetic layer. For example, Japanese Unexamined Patent Publication (Kokai) No. 1-189025 discloses that an acid, an alkali metal salt, a quaternary ammonium salt is used for a magnetic layer comprising a mono- or di-ester or an organic phosphorus compound selected from substituted or unsubstituted alkyl, alkenyl and aryl groups. It describes salts and the like, and specifically, it has been proposed to improve dispersibility by using phenylphosphonic acid. However, there has been a problem in performing a high degree of dispersion of ferromagnetic powder suitable for high-density recording. JP-A-58-171720 describes a magnetic recording medium in which a magnetic layer contains an alkyl phosphate having 6 or more carbon atoms. However, there is no description that a magnetic recording medium having excellent characteristics can be obtained by combining an alkyl phosphate and a specific ferromagnetic powder.

Japanese Patent No. 2566089 describes that a non-magnetic layer is provided with a magnetic recording medium containing a metal oxide and an organic acid having a pKa ≦ 3. This is characterized in that it contains an organic compound other than a fatty acid that can be adsorbed or reacted with the inorganic powder contained in the lower nonmagnetic layer,
It is stated that the compound capable of adsorbing is effective for organic acids having pKa ≦ 3. However, as the organic phosphoric acid compound, only aromatic phosphorus compounds such as phenylphosphoric acid and phenylphosphonic acid are described, and description of aliphatic phosphorus compounds is not given. Absent.

[0006]

According to the present invention, a non-magnetic coating layer comprising at least one non-magnetic powder and a binder dispersed therein is provided on at least one surface of a non-magnetic support. The present invention relates to a magnetic recording medium having a lower non-magnetic layer provided with a magnetic layer in which a binder is dispersed, and further provides a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability. It is assumed that.

[0007]

An object of the present invention is to provide a lower layer containing a nonmagnetic powder or a ferromagnetic powder and a binder on a nonmagnetic support, and disperse the ferromagnetic powder in the binder on the lower layer. In a magnetic recording medium provided with at least one magnetic layer as described above, the magnetic layer contains an aromatic organic phosphorus compound represented by the following general formula (1) or (2), and [(R ¹ ) _m -φ -O] _n -P (= O) (OH) _3-n (1) [(R ¹ ) _m -φ] _n -P (= O) (OH) _3-n (2) where R ^{1 is} substituted Or an unsubstituted alkyl group, aryl group, or aralkyl group. φ: represents a benzene ring.
n = 1, 2, m = 0, an integer of 1 to 5 (however, when m ≧ 2, R ¹ may be the same or different) The lower layer is represented by the following general formula (3) or (4) A magnetic recording medium containing an aliphatic organic phosphorus compound. _{^{[R 2 -O] k -P (}} = O) (OH) 3-k (3) [R 2] k -P (= O) (OH) 3-k (4) provided that, R ^2: a substituted or unsubstituted R ¹ represents a substituted alkyl group
May be the same or different. k = 1, 2 (where k
In the case of = 2, R ² may be the same or different.) The ferromagnetic powder contained in the magnetic layer contains Fe as a main component, 10 to 40 at% of Co, and 2 to 20 at% of Al.
%, Y is 1 to 15 at%.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention has a lower layer containing a nonmagnetic powder or a ferromagnetic powder and a binder on a nonmagnetic support, and the ferromagnetic powder is dispersed in the binder on the lower layer. In a magnetic recording medium provided with at least one magnetic layer, a specific organic phosphorus compound is used as a dispersant in the magnetic layer and a specific aliphatic organic phosphorus compound is contained in a lower layer to disperse the ferromagnetic powder. It is an object of the present invention to provide a magnetic recording medium having improved magnetic properties and excellent electromagnetic conversion characteristics.

The organic phosphorus compound which can be used as a dispersant in the present invention is represented by the following general formula. [(R ¹ ) _m -φ-O] _n -P (= O) (OH) _3-n (1) [(R ¹ ) _m -φ] _n -P (= O) (OH) _3-n ( 2) Here, R ^{1 represents a} substituted or unsubstituted alkyl group, aryl group, or aralkyl group. φ: represents a benzene ring.
n = 1, 2; m = 0, an integer of 1 to 5 (however, when m ≧ 2, R ¹ may be the same or different) The lower layer is represented by the following general formula (3) or (4) A magnetic recording medium comprising an aliphatic organic phosphorus compound to be used. _{^{[R 2 -O] k -P (}} = O) (OH) 3-k (3) [R 2] k -P (= O) (OH) 3-k (4) provided that, R ^2: a substituted or unsubstituted R ¹ represents a substituted alkyl group
May be the same or different. k = 1, 2 (However, when k = 2, R ² may be the same or different.) The alkyl group used as R ¹ and R ² has a carbon number in the range of 1 to 22. Those having a carbon number of 4 to 18 are particularly preferable. Specifically, a methyl group, an ethyl group, an (iso) propyl group, an (iso, s-, t-) butyl group, an (iso, neo, t-) pentyl group, a 1-methylbutyl group,
(Iso) hexyl group, (iso) heptyl group, (iso) octyl group, 2-ethylhexyl group, (iso) nonyl group,
Examples thereof include (iso) decyl group, (iso) undecyl group, (iso) dodecyl group, (iso) hexadecyl group, (iso) octadecyl group, and (iso) eicosyl group. Among the above specific examples, t-butyl group, octyl group,
A 2-ethylhexyl group, a dodecyl group and the like are particularly preferred.

The aryl group used as R ¹ includes phenyl, toluyl, xylyl, ethylphenyl, cumenyl, 4-biphenylyl and the like. Examples of the aralkyl group include a benzyl group, a phenethyl group, an α-methylbenzyl group, a 1-methyl-1-phenethyl group, and a diphenylmethyl group. Examples other than the hydrocarbon group include a methoxy group, a butoxy group, an amino group, a nitro group and F, Cl, Br, CF ₃ , CC
Examples thereof include halogen-containing hydrocarbons such as l ₃ and CBr ₃ . Further, an alkyl group, an aryl group, or an aralkyl group substituted with a group other than the above-mentioned hydrocarbon group may be used.

Among the above specific examples, a substituent having an aromatic ring is preferable, and a phenyl group, a benzylphenyl group and a 1-methyl-1-phenethyl group are particularly preferable. Specifically, examples of the aromatic phosphorus compound represented by the general formula (1) or (2) that can be used as a dispersant include the following compounds.

[0012]

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Further, as the aliphatic organic phosphorus compound represented by the general formula (3) or (4) suitable for the lower layer, the following compounds can be exemplified.

[0014]

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Such an organic phosphorus compound has a property of being adsorbed or bound by the above-mentioned polar group, and is mainly located on the surface of the ferromagnetic powder in the magnetic layer, and is mainly located on the non-magnetic powder in the non-magnetic layer. It is presumed that they exist in a state of being adsorbed or bonded by the polar group on the surface of the polymer. In particular, the adsorptive power of metal surfaces, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. on metal compound surfaces is higher than that of carboxylic acids and sulfonic acids. Since the organic phosphoric acid compound used in the present invention has a strong adsorbing power, the organic phosphorus compound once adsorbed is difficult to desorb from the surface of the metal or the metal compound. Therefore, the surface of the ferromagnetic powder or non-magnetic powder of the present invention is in a state in which the organophosphorus compound is strongly adsorbed and is covered with an aromatic ring or the like. It is presumed that the affinity for the ferromagnetic powder or non-magnetic powder is improved, and the dispersion stability of the ferromagnetic powder or non-magnetic powder is also improved.

Further, since the ferromagnetic powder or non-magnetic powder and the binder cause a strong interaction due to the action of the organic phosphorus compound, desorption of the ferromagnetic powder or non-magnetic powder does not occur, so that the running property and running durability can be improved. It is considered that the property is significantly improved. Furthermore, since the organic phosphorus compound used in the present invention has lower water absorption than other organic compounds such as sulfonic acid, it has good water resistance and durability. Also, since the thickness of the magnetic layer is about 0.2 μm, which is extremely thin compared to about 2 μm of the lower non-magnetic layer, the surface property of the magnetic layer that directly contacts the recording / reproducing head largely reflects the surface property of the lower non-magnetic layer. You.

As described above, in the present invention, an aromatic organic phosphorus compound is used for the upper magnetic layer as the organic phosphorus compound, and an aliphatic organic phosphorus compound is used for the lower non-magnetic layer. Compared to when an aromatic phosphorus compound or an aliphatic phosphorus compound is used for the lower non-magnetic layer, a magnetic recording medium with excellent magnetic properties, excellent smoothness on the surface of the magnetic recording medium, and excellent electromagnetic conversion characteristics, durability and storability can be obtained. I understood. This is because aromatic phosphorus compounds have better dispersibility of magnetic powders and non-magnetic powders than aliphatic phosphorus compounds, but the moldability in the calendering step performed for the purpose of further improving the smoothness is reduced. It is considered that the aromatic phosphorus compound is better than the aromatic phosphorus compound.

According to the present invention, the dispersibility of the upper magnetic powder is improved by using an aromatic phosphorus compound in the upper magnetic layer, and the calender is improved by using the aliphatic phosphorus compound in the lower nonmagnetic layer. Since the moldability in the process is improved, a magnetic recording medium having excellent electromagnetic conversion characteristics, durability and storage stability is provided.

In the magnetic layer or the lower non-magnetic layer of the present invention, the organic phosphorus compound is contained in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder or the non-magnetic powder. include. Especially when its content is 0.5
By setting the content within the range of ~ 15 parts by weight, a phenomenon such as an increase in the glossiness of the surface of the magnetic layer or the non-magnetic layer appears,
It can be seen that the ferromagnetic powder or non-magnetic powder has a good dispersion state. Further, by setting the content in the range of 1 to 10 parts by weight, the electromagnetic conversion characteristics are remarkably improved. If the content is less than 0.1 part by weight, the effect of the compounding may not be effectively exhibited, and if the content is more than 20 parts by weight, the dispersion state of the ferromagnetic powder or the nonmagnetic powder is further improved. May not.

As a method for improving the dispersibility of the ferromagnetic powder or non-magnetic powder by incorporating the above-mentioned organic phosphorus compound into a magnetic layer or a non-magnetic layer, the organic phosphorus compound is dissolved in a low boiling organic solvent or After the ferromagnetic powder or non-magnetic powder is prepared by dispersing the ferromagnetic powder or non-magnetic powder into the solution and mixing, the organic solvent is removed to prepare the ferromagnetic powder or non-magnetic powder pretreated with the organic phosphorus compound. A method for producing a magnetic recording medium using the treated ferromagnetic powder, and when preparing a coating solution for a magnetic layer or a coating solution for a non-magnetic layer, the organic phosphorus compound is directly or preferably used for the magnetic layer. A method of kneading and dispersing the mixture by dissolving or dispersing it in a part of the solvent for the coating liquid or the coating liquid for the nonmagnetic layer can be used. When the organic phosphorus compound of the present invention is kneaded and dispersed in a solvent with a magnetic or non-magnetic powder, it is extremely strongly adsorbed on the powder surface.

As the ferromagnetic metal powder used in the present invention, if the main component is Fe (including an alloy),
Although not particularly limited, a ferromagnetic alloy powder containing α-Fe as a main component is preferable. These ferromagnetic powders include Al, Si, S, Sc, Ca, Ti, V, Cr,
Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, T
e, Ba, Ta, W, Re, Au, Hg, Pb, Bi,
La, Ce, Pr, Nd, P, Co, Mn, Zn, N
It may contain atoms such as i, Sr, and B. Al,
Preferably, at least one of Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is contained in addition to α-Fe, and particularly preferably, Co, Al, and Y are contained. More specifically, it is preferable that Co contains 10 to 40 atom%, Al contains 2 to 20 atom%, and Y contains 1 to 15 atom% with respect to Fe.

These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent and the like before dispersion before dispersion. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The water content of the ferromagnetic powder is preferably 0.01 to 2%. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. Crystallite size is 8-20n
m, preferably 10 to 18 nm, particularly preferably 12 to 16 nm. The major axis diameter is measured by taking a transmission electron micrograph, and directly reading the short axis diameter and the long axis diameter of the ferromagnetic powder from the photograph, or by reading the transmission electron micrograph with an image analyzer. Is also good.

The crystallite size is calculated from the half width of the diffraction peak measured by an X-ray diffractometer.
It is the average value obtained by the method. Further, the major axis length of the ferromagnetic metal powder is 0.05 to 0.13 μm, preferably 0.07 to 0.12 μm, particularly preferably 0.07 to 0.12 μm.
8 to 0.11 μm. The specific surface area (S _BET ) of the ferromagnetic powder used in the magnetic layer of the present invention by the BET method is 30.
m ² / g or more 50m less than ² / g are preferred. And 38
４８48 m ² / g is preferred. This makes it possible to achieve both good surface properties and low noise.

It is preferable that the pH of the ferromagnetic powder be optimized depending on the combination with the binder used. The range is 4-1
2, but preferably 7 to 10. If necessary, the ferromagnetic powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof. The amount thereof is 0.1 to 10% based on the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr, but if it is 200 ppm or less, there is little influence on the characteristics. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less. The shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the above-mentioned characteristics regarding the particle size are satisfied. In the case of acicular ferromagnetic powder, the acicular ratio is preferably from 4 to 12 and more preferably from 5 to 12.

The thickness of the magnetic layer is high, especially 20 MHz.
In order to improve input / output characteristics at high frequencies exceeding
It is required to be 0.5 to 0.5 μm, preferably 0.1 to 0.5 μm.
It is 0.3 μm, more preferably 0.11 to 0.27 μm. To stably apply this ultra-thin magnetic layer, a lower non-magnetic layer containing inorganic powder is interposed on the support,
It is desirable to apply a magnetic layer thereon on a wet-on-wet basis. The coercive force Hc of the ferromagnetic metal powder is preferably 155.2-218.8 kA / m (1950-2
750 Oe), more preferably 159.2 to 18
At 3.0 kA / m (2000-2300 Oe), σs
Is preferably 140 to 170 Am ² / kg, and more preferably 145 to 160 Am ² / kg. The shape of the ferromagnetic powder is not particularly limited, but usually a needle shape, a granular shape, a dice shape, a rice grain shape, a plate shape or the like is used. It is particularly preferable to use acicular ferromagnetic powder.

The magnetic recording medium of the present invention may be formed on a non-magnetic support.
Has a lower non-magnetic layer coating layer consisting of a binder and non-magnetic powder.
I do. Non-magnetic powder that can be used for the lower non-magnetic layer is inorganic
However, it may be an organic substance. Also use carbon black etc.
Can be used. Examples of inorganic substances include metals and metal oxides.
Material, metal carbonate, metal sulfate, metal nitride, metal carbide
And metal sulfides. Specifically, titanium dioxide
Titanium oxide, cerium oxide, tin oxide, titanium oxide
Ngustene, ZnO, ZrO_Two, SiO_Two, Cr_TwoO_Three, Α
Α-alumina, β-alumina, γ with a conversion of 90 to 100%
-Alumina, α-iron oxide, goethite, corundum, nitrogen
Silicon carbide, titanium carbide, magnesium oxide,
Iodine, molybdenum disulfide, copper oxide, MgCO_Three, CaC
O_Three, BaCO _Three, SrCO_Three, BaSO_Four, Silicon carbide,
Titanium carbide etc. alone or in combination of two or more
used. Preferred are α-iron oxide and titanium oxide.
is there.

The shape of the nonmagnetic powder may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The crystallite size of the nonmagnetic powder is preferably 0.004 μm to 1 μm, and 0.04 μm
To 0.1 μm is more preferable. If it is smaller than 0.004 μm, dispersion tends to be difficult. If it is larger than 1 μm, the surface roughness tends to increase.

The average particle size of these nonmagnetic powders is 0.005.
The thickness is preferably about 2 μm, but if necessary, non-magnetic powders having different average particle diameters may be combined, or even a single non-magnetic powder may have the same effect by broadening the particle diameter distribution. Particularly preferred is 0.01 to 0.2 μm. 0.0
If it is smaller than 05 μm, dispersion tends to be difficult, and if it is larger than 2 μm, the surface roughness tends to increase. The specific surface area of the nonmagnetic powder is 1 to 100 m ² / g, preferably 5 to 70 m ² / g. And more preferably it is 10-65 m < ² > / g. Tend to 1 m ² / g smaller than the surface roughness becomes large, 100 m ²
If it is larger than / g, the dispersion tends to be difficult, for example, the desired amount of binder cannot be dispersed.

The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 8 ml.
0ml / 100g, more preferably 20-60ml / 1
00 g. The specific gravity is 1 to 12, preferably 3 to 6. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. If it is less than 0.05 g / ml, the amount of particles scattered tends to be large, making the operation difficult. If it is larger than 2 g / ml, it tends to stick to the device and the operation tends to be difficult.

The pH of the nonmagnetic powder is preferably from 2 to 11, but the pH is particularly preferably from 6 to 9. If the pH is less than 2, the friction coefficient under high temperature and high humidity tends to increase. On the other hand, when the pH is higher than 11, the release amount of the fatty acid decreases, and the friction coefficient tends to increase. The water content of the nonmagnetic powder is 0.1 to 5% by weight, preferably 0.2 to 5% by weight.
It is 3% by weight, more preferably 0.3 to 1.5% by weight. If it is less than 0.1% by weight, dispersion tends to be difficult. If it is more than 5% by weight, the viscosity of the paint after dispersion tends to be unstable.

The loss on ignition is preferably 20% by weight or less, and the loss on ignition is preferably small. When the nonmagnetic powder is an inorganic powder, the Mohs hardness is 4 or more,
Those having 10 or less are preferred. If the Mohs hardness is smaller than 4, durability tends to be insufficient.

The non-magnetic powder has a stearic acid adsorption amount of 1 to 2
0 μmol / m ² , more preferably ^{2 to} 15 μmol / m ²
m ² . The heat of wetting of the nonmagnetic powder in water at 25 ° C. is 0.2 J / m ^{2 to} 6 J / m ² (200 erg / cm ^{2 to} 6 J / m ² ).
00 erg / cm ² ). Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is 1 to 10
A piece / 10 nm is appropriate. PH of isoelectric point in water is 3
It is preferably between ９9 and ９9.

The surface of these non-magnetic powders has Al_TwoO_Three,
SiO_Two, TiO_Two, ZrO_Two, SnO_Two, Sb_TwoO_Three, Z
It is preferable to perform a surface treatment with nO 2. Particularly good for dispersibility
Al is better_TwoO_Three, SiO_Two, TiO_Two, ZrO_TwoIn
But more preferably Al_TwoO _Three, SiO_Two, ZrO_Two 
It is. These may be used in combination or used alone
Can also be. Also, coprecipitated surface according to the purpose
A treatment layer may be used, or after first treating with alumina
A method of treating the surface layer with silica or vice versa
Can also be taken. Also, the surface treatment layer depends on the purpose
Although it may be a porous layer, it is generally better to be homogeneous and dense
Is preferred.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and DPN-2 manufactured by Toda Kogyo.
50, DPN-250BX, DPN-245, DPN-
270BX, DPB-550BX, DPN-550RX
Titanium oxide TTO-51B, TTO-55 manufactured by Ishihara Sangyo
A, TTO-55B, TTO-55C, TTO-55
S, TTO-55D, SN-100, MJ-7, α-iron oxide E270, E271, E300, ST manufactured by Titanium Industry
T-4D, STT-30D, STT-30, STT-6
5C, Teika MT-100S, MT-100T, MT
-150W, MT-500B, MT-600B, MT-
100F, MT-500HD. Sakai Chemical FINEX-2
5, BF-1, BF- 10, BF-20, ST-M, Dowa Mining Ltd. DEFIC-Y, DEFIC-R, manufactured by Japan Aerosil AS2BM, TiO ₂ P25, manufactured by Ube Industries, Ltd. 100
A, 500A, Y-LOP manufactured by Titanium Kogyo Co., Ltd. and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

The lower non-magnetic layer is coated with a non-magnetic powder together with a non-magnetic powder.
By mixing Bon Black, the surface electric resistance (Rs) can be reduced, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. The micro Vickers hardness of the lower non-magnetic layer is usually 25 to 60.
kg / mm ² , preferably 294-490 MPa (30-50 kgf / mm
² ) and a thin film hardness tester (NEC HMA-40)
0) can be measured using a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. It is standardized that the light transmittance is generally 3% or less for infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used.

[0036] The specific surface area of carbon black employed in the nonmagnetic layer of the present invention is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption amount from 20 to 40
0 ml / 100 g, preferably 30-200 ml / 10
0 g. Particle size of carbon black is 5-80n
m, preferably 10 to 50 nm, more preferably 10 to
40 nm. PH of carbon black is 2-10,
Moisture content is 0.1-10%, tap density is 0.1-1g /
ml is preferred. Specific examples of carbon black used in the present invention include BLACKPE manufactured by Cabot Corporation.
ARLS 2000, 1300, 1000, 900, 8
00, 880, 700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd., # 3050B, 3150B, 3250
B, # 3750B, # 3950B, # 950, # 650
B, # 970B, # 850B, MA-600, manufactured by Columbia Carbon, CONDUCTEX SC, RAVE
N 8800, 8000, 7000, 5750, 525
0,3500,2100,2000,1800,150
0, 1255, 1250, manufactured by Akzo Ketjen Black EC, and the like. Carbon black may be surface-treated with a dispersant or the like, grafted with a resin, or used, or a part of the surface may be graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in a range not exceeding 50% by weight based on the inorganic powder and in a range not exceeding 40% of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination. The carbon black which can be used in the non-magnetic layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

In the lower layer, an organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used.

Further, in the magnetic recording medium of the present invention,
An undercoat layer may be provided. By providing the undercoat layer, the adhesive strength between the support and the magnetic layer or the lower non-magnetic layer can be improved. As the undercoat layer, a polyester resin soluble in a solvent is used. The undercoat layer having a thickness of 0.5 μm or less is used. In the magnetic recording medium of the present invention, a polar group-containing vinyl chloride resin and a polar group-containing polyurethane resin can be used as a binder used for forming the lower nonmagnetic layer or the magnetic layer.

As the polar group of the present invention, -SO ₃ M, -PO (OM) ₂ , -COOM (M is used for the purpose of improving the dispersibility of the ferromagnetic fine powder and the non-magnetic powder. A hydrogen atom, an alkali metal or an ammonium salt), an amino group, or a quaternary ammonium base. Among them, -SO3M is particularly excellent in dispersibility and is preferable. The preferred polar group content is 1 × 10 ⁻⁵ to 50 × 10 ⁻⁵ eq / g, more preferably 1 × 10 ⁻⁴ to 1 × 10 ⁻⁶ eq / g-binder. If less than 1 × 10 ⁻⁵ eq / g, no effect can be obtained,
If it exceeds × 10 ⁻⁵ eq / g, the viscosity of the paint becomes high, the workability becomes extremely poor, and the handling becomes difficult. Furthermore, polar groups to be introduced may be two or more, for example, in addition to be performed to introduce -COOM of -SO ₃ M.

The method for introducing a polar group into a polar group-containing vinyl chloride resin used in the present invention can be synthesized by, for example, adding the polar group to a vinyl chloride resin containing no polar group by a reaction. Specifically when introducing a -SO ₃ M vinyl chloride resin was initially copolymerizing these with other copolymerizable compounds and optionally copolymerizable compounds having a vinyl chloride monomer and a glycidyl group At the same time as the copolymerization or after obtaining the copolymer, and then reacting with a compound having -SO3M. Examples of the copolymerizable compound for introducing a glycidyl group include glycidyl acrylate, glycidyl methacrylate, and glycidyl vinyl ether, and these may be used alone or in combination of two or more.

Further, a copolymerizable polar group-containing compound may be copolymerized with a vinyl chloride monomer and other copolymerizable compounds. As the copolymerizable polar group-containing compound, a copolymerizable compound containing the polar group can be used. The copolymerizable compound for introducing a -SO ₃ M 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acrylic acid, methacrylic acid, unsaturated hydrocarbons such as p- styrenesulfonate Sulfonic acid and salts thereof, and acrylic acid or methacrylic acid sulfoalkyl esters such as methacrylic acid sulfoethyl ester and methacrylic acid sulfopropyl ester, and salts thereof can be given. These may be used alone or in combination of two or more. Further, when the polar group to be introduced is two or more, for example, the -SO ₃ besides copolymerizable compounds containing -COOM when introducing -COOM is required M, specifically acrylic acid, Methacrylic acid, maleic acid, and the like, and salts thereof can be used.

The polar group-containing vinyl unit of the polar group-containing vinyl chloride resin used in the present invention is 0.05 to 5% by weight.
Is less than 0.05% by weight, there is no effect of improving the dispersibility of the nonmagnetic powder or the magnetic powder.
On the other hand, if it exceeds 5% by weight, the viscosity of the coating material becomes high, and the pot life when the isocyanate compound is added becomes short.

57 to 98% by weight of vinyl chloride unit
Is preferred. If the amount is less than 57% by weight, the strength of the obtained resin coating film is reduced. Other copolymerizable monomers include vinyl acetate, vinyl propionate, (meth) acrylic acid ester, (meth) acrylic acid, (anhydrous) maleic acid, acrylonitrile, vinylidene chloride, hydroxyethyl (meth) acrylate, glycidyl (meth) Acrylate and the like can be mentioned.
Here, (meth) acryl means a material containing at least one of acryl and methacryl, and (maleic anhydride) means a material containing at least one of maleic acid and maleic anhydride. When other vinyl units are contained, the content is preferably 26% by weight or less. If it exceeds this range, the mechanical properties and dispersibility of the entire resin will be reduced.

The obtained vinyl chloride copolymer can be saponified to convert vinyl acetate, vinyl propionate, etc. into a vinyl alcohol component. The content of the vinyl alcohol unit is preferably 2 to 16% by weight. If the amount is less than 2% by weight, solubility of the coating material in organic solvents such as ketones and esters, dispersibility of non-magnetic powder and magnetic powder, reactivity with the isocyanate compound used in combination with the present resin, etc. No effect on the compatibility with the resin can be obtained, and if it exceeds 16% by weight, the viscosity of the coating becomes too high, and the pot life when the isocyanate compound is added becomes short, which is disadvantageous in practical use.

The average polymerization degree of the polar group-containing vinyl chloride resin used in the present invention is preferably from 200 to 800. Further, 250 to 700 is preferable. If it is less than 200, the resulting magnetic coating film becomes brittle, and the resulting magnetic coating film becomes brittle, so that the physical strength is reduced and the durability of a magnetic tape or the like is affected. If it exceeds 800, the viscosity of the paint at a predetermined concentration becomes high, the workability becomes extremely poor, and the handling becomes difficult.
The polar group-containing vinyl chloride resin used in the present invention is produced by adding compounds such as a polymerization initiator, a suspension stabilizer, an emulsifier, and a molecular weight modifier.

The polar group-containing polyurethane resin of the present invention comprises
It can be produced from a polar group-containing polyol such as a polyester polyol having a polar group, a polycarbonate polyol or a polyether polyol, and a polyol having no polar group such as a polyester polyol, a polycarbonate polyol or a polyether polyol, and a diisocyanate. For example, it can be produced by changing a part of dihydric alcohol or dibasic acid to polar group-containing diol or polar group-containing dibasic acid. The polar group-containing polyol has a polar group represented by the above general formula in the main chain or side chain of the polyol described below.

The above polyester polyol is, for example,
Examples thereof include those obtained by polycondensation of a dihydric alcohol and a dibasic acid, and those obtained by ring-opening polymerization of lactones, for example, caprolactone. Typical dihydric alcohols include glycols such as ethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, and cyclohexanedimethanol. Typical dibasic acids include adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, and the like. Further, the polycarbonate polyol has a molecular weight of 300 to 20,000 synthesized by condensation or transesterification of a polyhydric alcohol with phosgene, chloroformate, dialkyl carbonate or diallyl carbonate, and a hydroxyl value of 2
A polycarbonate polyol having a molecular weight of 400 to 30,000 and a hydroxyl value of 5 obtained by condensation of a polycarbonate polyol having a molecular weight of 100 to 300 or the polycarbonate polyol with a divalent carboxylic acid.
~ 300 polycarbonate polyester polyols. Examples of the polyether diol include polyethylene oxide and / or polypropylene oxide adducts such as bisphenol A, hydrogenated bisphenol A, bisphenol S and bisphenol P, and polyethers having a molecular weight of 500 to 5,000 such as polypropylene glycol, polyethylene glycol and polytetramethylene glycol Polyols can be used.

As the polyol, bisphenol A,
Polyether polyols containing hydrogenated bisphenol A and their ethylene oxide and propylene oxide adducts and containing ether groups in the range of 25% by weight to 45% by weight, more preferably 30% by weight to 40% by weight are preferred. If the content is less than 25% by weight, the solubility in a solvent is reduced, and the dispersibility is reduced. If it exceeds 45% by weight, the strength of the coating film is reduced, so that the durability is reduced. Other polyols may be blended with the above polyol up to 90% by weight of the above polyol and used in combination.

As the polyisocyanate used to form the polyurethane by reacting with the above-mentioned polyol, a commonly used polyisocyanate can be used.
For example, hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3
-Xylylene diisocyanate, 1,4-xylylene diisocyanate cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4 ′
-Diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate,
Examples thereof include 1,5-naphthalenediisocyanate and 3,3-dimethylphenylenediisocyanate.

As the chain extender, polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like can be used. Among them, polyhydric alcohols having a molecular weight of 50 to 500 are preferable. If it is less than 50, the coating film becomes brittle and the durability is reduced. If it is 500 or more, the glass transition temperature (Tg) of the coating film decreases, and the coating film becomes soft, so that the durability decreases.

Examples of polyhydric alcohols include bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, and ethylene oxide and propylene oxide adducts thereof, cyclohexanedimethanol, cyclohexanediol, hydroquinone, and bis (2-hydroxyethyl) tetrabromobisphenol. A, screw (2
-Hydroxyethyl) tetrabromobisphenol S,
Bis (2-hydroxyethyl) tetramethylbisphenol S, bis (2-hydroxyethyl) diphenylbisphenol S, bis (2-hydroxyethyl) diphenylbiphenol, bis (2-hydroxyethyl) thiodiphenol, bis (2-hydroxyethyl ) Short-chain diols having a cyclic structure such as bisphenol F, biphenol, bisphenol fluorene, and bisphenol fluorene hydroxyethyl ether are preferred. More preferred are bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and diols having an aromatic or alicyclic group such as ethylene oxide, propylene oxide adduct thereof, cyclohexane dimethanol and cyclohexane diol.

The average molecular weight of the polar group-containing polyurethane resin used in the present invention is preferably 5,000 to 100,000. Further, it is preferably 10,000 to 50,000. 500
If it is less than 0, the resulting magnetic coating film becomes brittle, and the resulting magnetic coating film becomes brittle, resulting in a decrease in physical strength, which also affects the durability of a magnetic tape or the like. In addition, the molecular weight is 100,000
If it exceeds, the solubility in a solvent is reduced, and the dispersibility is reduced. Further, the viscosity of the paint at a predetermined concentration becomes high, so that workability is remarkably deteriorated and handling becomes difficult. As the OH group of the polar group-containing polyurethane resin used in the present invention,
It is preferable to have a branched OH group from the viewpoint of curability and durability, and it is preferably 2 to 40 per molecule, and more preferably 3 to 20 per molecule.

As other binders used in the present invention, together with the above-mentioned polar group-containing vinyl chloride resin and polar group-containing polyurethane resin, the other polar groups are further added in an amount equal to or less than the total amount of these. You may use together the binder which has. As other resins that can be used in combination, thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof, which have been conventionally used as a binder for magnetic recording media, can be used. Specifically, as the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1,000 to 200,000, preferably 1,000.
It has a degree of polymerization of about 0 to 100,000 and a degree of polymerization of about 50 to 1,000. Examples of such a polymer include acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, a polymer containing vinyl ether, and the like as constituent units, and copolymers. There are coalescing, polyurethane resin and various rubber resins.
Further, as the thermosetting resin or the reactive resin, phenol resin, phenoxy resin, epoxy resin, urea resin,
Examples include melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, and mixtures of polyester resins and isocyanate prepolymers.

In the magnetic recording medium of the present invention, the magnetic layer or the lower non-magnetic layer has a lubricating effect, an antistatic effect,
An additive for providing a dispersing effect, a plasticizing effect, and the like may be contained. These additives include molybdenum disulfide,
Tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, polar group silicone,
Fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and Its alkali metal salt, carbon number 1
Monobasic fatty acids which may contain 0 to 24 unsaturated bonds and may be branched, and metal salts thereof (Li,
Na, K, Cu, etc.) or containing an unsaturated bond having 12 to 22 carbon atoms, or a branched or branched 1 to 6 alcohol, containing an unsaturated bond having 12 to 22 carbon atoms,
In addition, an alkoxy alcohol which may be branched, containing an unsaturated bond having 10 to 24 carbon atoms, or containing a monobasic fatty acid which may be branched and an unsaturated bond having 2 to 12 carbon atoms, Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester composed of any one of 1 to 6 alcohols which may be a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, a fatty acid amide having 2 to 22 carbon atoms, An aliphatic amine having 8 to 22 carbon atoms can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, myristin Octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol.

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums and Cationic surfactants such as sulfoniums, carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group,
Anionic surfactants containing acidic groups such as amino acids,
Aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohols, and alkyl betaine-type amphoteric surfactants can also be used. For these surfactants,
It is described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components.
These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

The types and amounts of these lubricants and surfactants used in the present invention can be selected as needed in the non-magnetic layer and the magnetic layer. For example, to control bleeding to the surface using fatty acids having different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface using esters having different boiling points and polarities, and to adjust the amount of surfactant. It can be considered to improve the stability of coating and improve the lubricating effect by increasing the amount of the lubricant added to the non-magnetic layer. Of course, the present invention is not limited to the examples shown here. Further, all or a part of the additives used in the present invention may be added in any step of producing a coating solution for the magnetic layer or the lower layer. For example, when mixing with a ferromagnetic powder before a kneading step, when adding in a kneading step with a ferromagnetic powder, a binder and a solvent, when adding in a dispersing step, when adding after dispersing, when adding just before coating, and the like. There is.

Specific examples of the lubricants used in the present invention include NAA-102, castor oil-hardened fatty acid, NAA-42, cation SA, Nymeen L-201, Nonion E-208, manufactured by NOF Corporation. Anon BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku: oleic acid, manufactured by Takemoto Yushi: FA
L-205, FAL-123, Nippon Rika Co., Ltd .: Nujielbu OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Armor Co .: Armide P, Lion Co., Ltd., Duomin TD
O, manufactured by Nisshin Oil Co., Ltd .: BA-41G, manufactured by Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionnet MS-400.

The coating solution prepared from the above materials is coated on a non-magnetic support to form a lower coating layer or a magnetic layer. As a nonmagnetic support that can be used in the present invention, biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenzoxdazole, or the like can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports are treated in advance by corona discharge, plasma treatment, easy adhesion treatment,
Heat treatment or the like may be performed. Further, the nonmagnetic support which can be used in the present invention has a surface having excellent smoothness such that the center line average surface roughness is in the range of 0.1 to 20 nm, preferably 1 to 10 nm at a cutoff value of 0.25 mm. Is preferred. It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more. The arithmetic average roughness of the obtained support is the value of (Ra) [JIS B0660-1998,
[ISO 4287-1997] is preferably 0.1 μm or less because noise of the obtained magnetic recording medium is reduced. The preferred thickness of the non-magnetic support in the magnetic recording medium of the present invention is 3 to 80 μm.

A backcoat layer (backing layer) is formed on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied.
May be provided. The back coat layer is provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on a surface of the non-magnetic support on which the magnetic paint is not applied. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . An adhesive layer may be provided on the surface of the non-magnetic support of the present invention where the magnetic paint and the back coat layer forming paint are applied.

In the method for producing a magnetic recording medium of the present invention, for example, a magnetic coating solution is applied to the surface of a running non-magnetic support so as to have a predetermined thickness. Here, a plurality of magnetic layer coating solutions may be sequentially or simultaneously multi-layer coated, or a lower layer coating solution and a magnetic layer coating solution may be sequentially or simultaneously multi-layer coated. Coating machines for applying the above magnetic coating solution or lower layer coating solution include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, and kiss coat. , Cast coat, spray coat, spin coat and the like can be used.

For these, for example, “Latest Coating Technology” (May 31, 1983) published by Sogo Gijutsu Center can be referred to. When applied to the magnetic recording medium of the present invention, the following can be proposed as an example of a coating apparatus and method. (1) The lower layer is first applied by a coating device such as gravure, roll, blade, or extrusion which is generally applied in coating of the magnetic layer coating solution, and the lower layer is dried while the lower layer is in an undried state. No., JP-A-60-238
No. 179, JP-A-2-265672, etc., the upper layer is applied by a support pressure type extrusion coating apparatus. (2) JP-A-63-88080, JP-A-2-179
No. 71 and Japanese Patent Application Laid-Open No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965. The coating layer of the magnetic layer coating solution is dried after subjecting the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution to a magnetic field orientation treatment.

After drying as described above, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyamideimide is used. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a center line average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
It is preferable that the surface has an extremely excellent smoothness of 4 nm, preferably 1 to 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the above calendering treatment. As the calendering conditions, the temperature of the calender roll is in the range of 60 to 100 ° C, preferably in the range of 70 to 100 ° C, particularly preferably 80 to 10 ° C.
0 ° C. range, pressure 98.0-490 kN / m
(100-500 kgf / cm), preferably 196-441 kN / m (200-450 kgf / cm).
cm, particularly preferably 29
It is preferable to perform the operation by operating under the condition of 4 to 392 kN / m (300 to 400 kgf / cm). The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

The magnetic recording medium of the present invention uses an aliphatic organic phosphorus compound for improving dispersibility in the lower non-magnetic layer, so that the influence of the surface roughness of the support and the influence of the surface roughness of the lower layer are improved. Thus, the surface smoothness of the upper magnetic layer can be improved. Therefore, even in a magnetic recording medium such as a digital video recording system requiring higher density, it is possible to solve problems such as a decrease in reproduction output and an increase in errors due to dropout.

[0065]

The present invention will be described below with reference to examples. In the examples, "parts" indicates "parts by weight" unless otherwise specified. Example 1 (Preparation of upper magnetic coating liquid) 100 parts of ferromagnetic alloy powder (composition: Fe / Co / Al / Y = 68/20/7/5, surface treatment agents: Al ₂ O ₃ , Y ₂ O ₃ , Hc: 189 kA / m (2380 Oe), crystallite size: 142 °, major axis diameter: 0.12 μm, needle ratio: 8, BET specific surface area: 46 m ² / g, σs: 152 Am ² / kg 12 parts of polyurethane resin ( UR8200: Toyobo, sulfonic acid group-containing polyurethane resin) Vinyl chloride resin 6 parts (MR110: ZEON, sulfonic acid group-containing vinyl chloride resin) Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (particle size 0) .15 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts 1 part stearic acid (Preparation of lower layer non-magnetic coating solution) non-magnetic inorganic powder (alpha-iron oxide) 85 parts (surface treatment _{agent: Al 2 O 3, SiO 2} , major axis length: 0.15 [mu] m, the tap density : 0.8, needle ratio: 7, BET specific surface area: 52 m ² / g, pH: 8, DBP oil absorption: 33 g / 100 g) Carbon black (particle size: 20 nm) 20 parts (DBP oil absorption: 120 ml / 100 g, pH: 8, BET specific surface area, 250 m ² / g, volatile matter: 1.5%) Polyurethane resin 12 parts (UR8200: manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin) Vinyl chloride resin 6 parts (MR110: manufactured by Nippon Zeon) a sulfonic acid group-containing vinyl chloride resin) α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 1 parts of phosphoric acid monolauryl 3 parts cyclohexanone 140 parts Methyl ethyl ketone 70 parts Butyl stearate 2 parts Stearic acid 1 part For each of the above-mentioned magnetic paint for upper layer and non-magnetic paint composition for lower layer, each component was kneaded with an open kneader for 60 minutes and then dispersed in a sand mill for 120 minutes. To the dispersion, 6 parts of a trifunctional low molecular weight polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane) is added, and the mixture is further stirred and mixed for 20 minutes, and then filtered using a filter having an average pore diameter of 1 μm to obtain a magnetic paint and a non-magnetic paint. Was prepared.

Further, the above-mentioned non-magnetic paint was applied so that the thickness after drying became 1.8 μm, and immediately thereafter, the magnetic paint was applied simultaneously and in layers so that the thickness after drying became 0.2 μm. In a state where both layers are not dried, a magnetic field orientation is performed with a 3000 Gauss magnet, and after drying, the speed is 100 m / mi using a seven-stage calender composed of only metal rolls.
n, linear pressure 294 kN / m (300 kg / cm), temperature 9
After performing a surface smoothing treatment at 0 ° C., a heat curing treatment was performed at 70 ° C. for 24 hours, and the resultant was cut into a 6.35 mm width to produce a magnetic tape.

Examples 2 to 10 The magnetic materials and dispersants were changed as shown in Table 1, and
Examples 2 to 10 were produced in the same manner as in Example 1.

Comparative Examples 1 to 7 The magnetic materials and dispersants were changed as shown in Table 1, and
Comparative Examples 1 to 7 were produced in the same manner as described above.

(Measurement Method) (1) Magnetic Properties [Small axis diameter and long axis diameter] A method of taking a transmission electron micrograph and directly reading the short axis diameter and the long axis diameter of the ferromagnetic powder from the photograph. And image analyzer (IB manufactured by Carl Zeiss)
ASSI) and a method of tracing and reading transmission electron micrographs. [Crystallite size] X-ray diffractometer (Rigaku RINT
The average value obtained by the Scherrer method from the half width of the diffraction peak under the conditions of a radiation source CuKα1, a tube voltage of 50 kV, and a tube current of 300 mA was used. (2) Electromagnetic conversion characteristics Output / output reduction: The obtained tape was heated at 23 ° C. and 50% RH.
Record a signal with a frequency of 4.7 MHz and reproduce it. The output at the time of the first reproduction was evaluated based on the output relative to the tape of Example 1. The output was continuously reproduced 1000 times more and the output was continuously reproduced. The output of each sample was set to 0 dB for the first output, and the output reduction was measured.

[0070]

[Table 1]

[0071]

As described above, according to the present invention, a non-magnetic coating layer in which at least a non-magnetic powder and a binder are dispersed is provided on at least one surface of a non-magnetic support. In a magnetic recording medium having a lower non-magnetic layer provided with a magnetic layer formed by dispersing a binder, at least at least a specific organic phosphoric acid compound is added to the lower non-magnetic layer, thereby improving the smoothness of the coating film. Electromagnetic conversion characteristics are improved, the surface of the magnetic layer is hardly scraped, head dirt is reduced, storage stability is greatly improved, dropout is reduced, running durability is excellent, and surface smoothness of the magnetic recording medium is excellent. As a result, it is possible to provide a magnetic recording medium capable of obtaining a high output, so that a remarkable effect is recognized as compared with the conventional method.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 CD021 DG001 EA011 HA066 JC22 JC23 KA20 NA22 5D006 BA05 BA09 EA01 FA02 FA05 FA09

Claims (2)

[Claims] An underlayer containing a nonmagnetic powder or a ferromagnetic powder and a binder is provided on a nonmagnetic support, and at least one or more magnetic layers in which the ferromagnetic powder is dispersed in the binder are provided thereon. In the magnetic recording medium, the magnetic layer contains an aromatic organic phosphorus compound represented by the following general formula (1) or (2), and [(R ¹ ) _m -φ-O] _n -P (= O) (OH) _3-n (1) [(R ¹ ) _m -φ] _n -P (＝ O) (OH) _3-n (2) where R ^{1 is a} substituted or unsubstituted alkyl group, aryl group, Represents an aralkyl group. φ: represents a benzene ring.
n = 1, 2, m = 0, an integer of 1 to 5 (however, when m ≧ 2, R ¹ may be the same or different) The lower layer is represented by the following general formula (3) or (4) A magnetic recording medium comprising an aliphatic organic phosphorus compound. _{^{[R 2 -O] k -P (}} = O) (OH) 3-k (3) [R 2] k -P (= O) (OH) 3-k (4) provided that, R ^2: a substituted or unsubstituted R ¹ represents a substituted alkyl group
May be the same or different. k = 1, 2 (where k
In the case of = 2, R ² may be the same or different) 2. The method according to claim 1, wherein the ferromagnetic powder contained in the magnetic layer is F
e as the main component, Co is 10 to 40 at%, and Al is 2 to
2. The magnetic recording medium according to claim 1, wherein 20 at% and Y are contained at 1 to 15 at%.