JPH04113510A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve output in long wavelength and short wavelength ranges and to improve C/N by forming an upper magnetic layer of a thin film containing Co-contg. iron oxide with high coercive force (Hc) and a lower magnetic layer having Hc less than 0. 8 time as that of the upper layer, and specifying the average center-line surface roughness of the upper layer to <=4nm. CONSTITUTION:The upper magnetic layer contains Co-contg. iron oxide as a ferromagnetic powder and has 1200-20000e coercive force and 0.05-0.8mum dry thickness. The lower magnetic layer contains Co-contg. iron oxide as a ferromagnetic powder and has the coercive force less than 0.9 time and more than 0.5 time of the coercive force of the upper layer. The upper layer has the average center-line surface roughness (Ra) of <=4nm. The minimum short recording wavelength of the medium is <=0.8mum. Thereby, large output is obtained from a very short wavelength region to a large wavelength region with improved C/N, and especially the output in a very short wavelength of <=0.8mum is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic recording medium comprising a non-magnetic support and a magnetic layer, and particularly to a magnetic recording medium having a multilayered magnetic layer. The invention particularly applies to 811IL
The present invention relates to a magnetic recording medium that is optimal for extremely short wave recording with a shortest recording wavelength of 0.8 μm or less, such as L1 video, digital VTR, and high-definition VTR1.

(Background of the Invention) There is a strong demand for smaller size and longer recording time for magnetic recording media, especially video tapes. Therefore, the shortest recording wavelength is 1 μm or less, particularly 0.1 μm in recent 8s videos, and especially 0.5 μm in Hi8, and there is a demand for improvement in electromagnetic conversion characteristics at extremely short wavelengths.

In the 8-kaku videotape, metal powder is used as the ferromagnetic powder. However, video tapes using metal powder have the following problems.

■High output but high noise (C/N (ratio of output to noise) is not necessarily high.

■The running durability of the magnetic layer is low, probably due to poor dispersibility and low bonding strength between the binder and the ferromagnetic powder.

■If stored for a long time at high temperature and humidity, the magnetic flux density will decrease due to the oxidation of ferromagnetic powder, resulting in a decrease in output.

■Ferromagnetic powder is expensive because it requires measures to prevent oxidation during manufacturing and transportation.

For this reason, magnetic recording media using cheaper iron oxide have been proposed, but the output is too low for ultrahigh-frequency recording, and the C/N and S/N are low, making them unusable. Ta.

In addition, in a single layer, if the coercive force (Hc) of the magnetic layer is increased to increase the output in the short wavelength region, the output in the long wavelength region will decrease, so It has been difficult to obtain a magnetic recording medium with desirable characteristics as a magnetic recording medium such as a video tape that requires output in a short wavelength range of 2 μ or less.

In order to solve problems such as output in long and medium wavelength regions and short wavelength regions, multilayer magnetic recording media have been proposed.

A known example related to Hc is JP-A-56-93123. In multilayer tape, the coercive force of the upper layer is 120 (1
~2000Oe, coercive force of lower layer 300~1000Oe
It is known above. However, in the above patent, the binder in the upper layer does not have a functional group, so the dispersibility of the ferromagnetic material is insufficient, and the surface roughness of the resulting magnetic layer is large, resulting in poor contact with the head and scratches. The pacing loss becomes large and the extremely short wavelengths required for high-density video are 0. Electromagnetic conversion characteristics of 8μ or less were not sufficient. Furthermore, since the upper layer had a thickness of 1μ or more, the characteristics of the lower layer of resistive magnetic force could not be fully brought out, and the output in the short and medium wavelength ranges of 1 to 4μ was low. The disclosure in the examples of this patent shows that the characteristics are improved in analog audio with a long wavelength (20KHz shortest wavelength for compact cassette = 2.4μ), but it is shown that the characteristics are improved in ultra short wave recording of 0.8μ or less. Equivalent examples regarding output and C/N are not shown.

Moreover, in JP-A-01-106333, the Hc of the upper layer is 120.
Since it is low at 0 Oe or less, it is not suitable for extremely short wavelength recording of 0.8 μ or less.

Furthermore, in JP-A-58-70429, the Hc of the upper layer is 140.
0 Oe tape is shown, but since the binder does not contain functional groups, the surface of the magnetic layer is relatively rough, and the 0.8μ
Not suitable for extremely short wavelength recording.

For this reason, in the example, the compact cassette is used at 10KHz.
Only the output at a wavelength of 4.8μ and the bias noise in analog bias recording are shown.

In addition, as a known example related to multilayer using iron oxide ferromagnetic powder, Japanese Patent Publication No. 51-29806 (upper layer/lower layer = CoFe20
3/Fe304), Special Publication No. 54-8286 (upper layer/lower layer = Co Fe203/Fe203), Special Publication No. 1986-
30608 (upper layer/lower layer-CoF e304/CoF
e203), JP-A-55-108928 (upper layer/lower layer =
Co iron oxide/magnetite) or Co? Gnetite), JP-A-56-143532 (upper layer/lower layer = mixed CoFeO
x/mixed ferromagnetic powder), JP-A-58-56230 (upper layer/lower layer - CoFe203/Fe203), JP-A-58-58
146025 (upper layer/lower layer-CoFeOx/Fe2
03), JP-A-58-159238 (upper layer/lower layer-C
oFeOx/Fe203) and the like are known.

The above-mentioned known examples disclose an iron oxide-based multilayer, but the Hc of the upper layer is low at 1200 Oe or less, and the examples have also been compared and studied for analog audio, and are suitable for extremely short wavelength recording of 0.8μ or less. Not suitable.

Furthermore, as a known example of a binder having a polar group, JP-A No. 6
3-261530 and JP-A-02-110825.

In the above-mentioned known examples, it is known to use a polar group-containing binder.

However, no magnetic recording medium has been shown that has a high output in the extremely short wavelength region of 0.8 μm or less by setting the coercive force of the upper layer to 1200 to 2000 Oe and the surface roughness of the magnetic layer to Ra of 4 nm or less.

Other known examples include JP-A-62-264728, JP-A-63-46324, JP-A-63-183345, and JP-A-63-261577.

Some of the above-mentioned known examples include partially known examples regarding iron oxide multilayers, Hc, etc.

However, no magnetic recording medium has been shown that has a high output in the extremely short wavelength region of 0.8 μm or less by setting the coercive force of the upper layer to 1200 to 2000 Oe and the surface roughness of the magnetic layer to Ra of 4 nm or less.

The present inventors have discovered that an excellent magnetic recording medium with a high C/N in an extremely short wavelength region can be obtained by using iron oxide ferromagnetic powder with a low noise level, and have arrived at the present invention.

(Object of the Invention) The object of the present invention is to provide a magnetic recording medium with high output and improved C/N over a range from extremely short wavelengths to long wavelengths, particularly a magnetic recording medium with improved output at extremely short wavelengths of 0.8μ or less. The goal is to provide recording media.

(Structure of the Invention) That is, the present invention provides a magnetic recording medium in which at least two magnetic layers in which ferromagnetic powder is dispersed in a binder are provided on a non-magnetic support.
The upper magnetic layer contains cobalt-containing iron oxide as ferromagnetic powder, and the coercive force of the upper magnetic layer is 1200 to 2000 Oe.
and has a dry thickness of 0.05 to 0.8μ, the lower magnetic layer contains cobalt-containing iron oxide as ferromagnetic powder, and the coercive force of the lower magnetic layer is 0 of the coercive force of the upper magnetic layer.
8 times or less, the centerline average surface roughness (Ra) of the upper magnetic layer is 4 nm or less, and the shortest recording wavelength of the magnetic recording medium is 0.8 μ or less. This can be achieved by recording media.

More preferably, the above object of the present invention is such that the binder has at least one of the following polar groups in the range of 10-' to 104
Contains vinyl chloride copolymer containing mol/g, and the total amount of binder including hardening agent is 15 to 30% of the ferromagnetic powder.
% by weight.

Polar group C00M, 503M, OSOHM, P
O(OM)z, NH-, OPO(OM)z Here, M represents hydrogen, an alkali metal, or an ammonium salt.

The above object of the present invention is to apply a magnetic paint in which cobalt-containing iron oxide and a binder are dispersed onto a non-magnetic support, to form at least two upper and lower magnetic layers, and after orientation and drying, the surface of the magnetic layer obtained is Between the calender rolls with Shore A hardness of 30 degrees or more, the temperature is 70 to 120 degrees Celsius, and the line pressure is 200 to 500 kg.
/c11, and the upper magnetic layer has a coercive force of 1200 to 2000 Oe and a dry thickness of 0.05 to 0.
．． This can be achieved by a method for manufacturing a magnetic recording medium characterized by obtaining a magnetic layer in which the coercive force of the lower magnetic layer is 0.8 times or less than the coercive force of the upper magnetic layer. In other words, metal magnetic powder has been considered as a magnetic recording medium suitable for high-density recording because it can easily provide high Hc and high output, but as mentioned above, it has poor dispersibility and high noise.
The C/N is relatively not so high, and the saturation magnetization (σS)
Due to the high . In recent years, the present inventors have discovered that it is possible to obtain high Hc iron oxide ferromagnetic powder by changing the amount of Co deposited, etc., and when we applied this to the upper layer of a multilayer magnetic layer, we found that The inherent good dispersibility of the iron oxide ferromagnetic metal powder is utilized as it is, and combined with the high Hc and extremely thin layer, the output and C/N in ultra-high frequency recording are improved. In other words, in the present invention, by including highly dispersible Co-containing iron oxide in the lower magnetic layer, an extremely smooth magnetic layer can be obtained. H
By combining it with the Co-containing iron oxide of c, a highly smooth magnetic layer was obtained in which the center line surface average roughness (Ra) of the upper magnetic layer was 4 nm or less. By adopting such a structure, for example, the upper magnetic layer has a 20°
o Fe metal powder of Oe is used, and the upper layer thickness is 1 μm
In cases like this, a binder with insufficient dispersibility is used, and therefore, as in the CIO sample of the present invention, 12 MHz or 1
The output at 5 MHz is degraded, and because the difference with the lower layer Hc is too large, the output at 6 MHz is degraded, resulting in a sagging phenomenon. Further, although the output of C/N increases, the noise also increases, so that a sufficient effect cannot be obtained as a whole. On the other hand, as shown in C9, by setting the thickness of the upper layer to 0.6 μm and using the same recipe as in the embodiment of the present invention, the output is improved, but the sag in the middle is not improved, and the C/N is not as good as its original ability. I am not able to demonstrate my full potential. On the other hand, by using the same high Hc ferromagnetic powder but CO-containing iron oxide powder, the dry thickness was reduced to 0.05 to 0.8.
By setting μ to further balance the Hc of the lower magnetic layer with the upper layer, the frequency can be increased from 0.5MHz to 15MHz.
It was surprising from the conventional idea of metal magnetic powder that not only the output was improved, but also the C/N from 8 MHz to 15 MHz was improved in a well-balanced manner.

Also, by setting the Ra of the upper magnetic layer to 4 nm or less,
Output and C/N at short wavelengths can be significantly improved. The dispersibility of such magnetic recording media can be further improved by combining a polar group-containing binder, and the excellent properties described above can be achieved by processing at a certain Shore A hardness, calender low mountain temperature, and linear pressure. A magnetic recording medium having the above structure can be effectively obtained.

Hc1200 to 2000O used in the upper layer of the present invention
The iron oxide ferromagnetic powder of e can be obtained by a conventionally known method,
Since it has a higher Hc than conventional general iron oxide ferromagnetic powder, it is preferable to obtain it as follows.

The amount of Co deposited on iron oxide is determined by the atomization (a) relative to Fe.
tm)% is preferably 6% or more, particularly preferably about 7% or more. When it is less than 6%, it becomes difficult to obtain the desired Hc. Moreover, if it exceeds about 20%, adhesion becomes difficult and the magnetic susceptibility (σS) decreases, which is not preferable.

The alkaline strength during the adhesion reaction is sodium hydroxide, NaOH.
It is preferable that the viscosity is 1 normal or more. If it is about 10 normal or more, the viscosity becomes high, which is difficult to handle, and the adhesion reaction tends to be uneven, so it is not preferable.

The temperature during the reaction is preferably 95°C or higher to the boiling point at the above alkali concentration.

The reaction time is preferably at least 1 hour, particularly preferably at least 5 hours.

Further, during the reaction, it is preferable to carry out the reaction in a nitrogen atmosphere to prevent oxidation of C01Fe.

Preferred embodiments of the present invention are as follows.

The Hc of the second magnetic layer (upper layer) is 1200 Oe to 2 (100
It is Oe. If the Hc of the upper layer is less than about 1200 Oe, the output and C/N in the extremely long wavelength region will be low, which is not preferable. Iron oxides with Hc exceeding about 2000 Oe are very difficult to obtain and are therefore not preferred.

The coercive force of the first magnetic layer (lower layer) is 0.9 times or less that of the second magnetic layer, preferably 0.9 times or less. 8 times or less 0. It is 5 times or more, particularly preferably 0.8 or less and 0.6 times or more.

If the coercive force of the lower layer exceeds about 0.9 times that of the upper layer, H
Since the c difference is small, the output in the long-lived wavelength range is undesirable, and if it is less than 0.5 times, the Hc difference between the upper and lower layers becomes too large, resulting in a noticeable drop in the output in the medium and short wavelength range. Undesirable.

The ferromagnetic powder used for the first and second layers is C.

The contained iron oxide may contain other trace elements if necessary. If Co is not included, the desired Hc cannot be obtained, which is not preferable.

The molar ratio of Fe'' and Fe3+ in iron oxide is o:io.

~so:ioo is preferred, especially 20:100~5o
:xoo is preferred.

The ferromagnetic powders used both have an average major axis diameter of 0°05μ~
It is preferable that the ferromagnetic powder used in the first magnetic layer has a larger average major axis diameter than the ferromagnetic powder used in the second magnetic layer because it is easier to disperse.

Furthermore, the major axis length of the ferromagnetic powder used in the present invention is 0.
It is 5μ or less, preferably 0.3μ or less. Also,
The major axis length of the ferromagnetic powder contained in the second layer is preferably smaller than the major axis length of the ferromagnetic powder contained in the second layer. The ratio of the short axis length to the long axis length, ie, the acicular ratio, is between 2 and 20. The long axis here means the longest axis of the three axes of the particle, and the short axis means the shortest axis.

Moreover, if the specific surface area of the ferromagnetic powder used in the present invention is expressed by the BET method, it is 25 to 80rr! /g, preferably 35 to 60 r+(/g. Below 25 rrf/g, the noise becomes high, and above 80 rrf/g, it is difficult to obtain good surface properties. Also, the ferromagnetic powder contained in the second magnetic layer It is preferable that the specific surface area of the ferromagnetic powder is larger than that of the ferromagnetic powder contained in the first layer because the noise level is lowered.The crystallite size of the ferromagnetic powder used in the present invention is 50 to 4.
50 angstroms, preferably 100 to 35 angstroms
0 angstrom. Further, it is preferable that the crystallite size of the ferromagnetic powder contained in the first layer is smaller than the crystallite size of the ferromagnetic powder contained in the second layer, since the noise level is lower.

The σS of the ferromagnetic powder used in the present invention is 5Qe+au/
g or more, preferably 7 Oemu/g or more, and the water content is preferably 0.01 to 2%. It is preferable to optimize the moisture content of the ferromagnetic powder within the range shown on the left depending on the type of binder.

It is preferable to optimize the pH of the ferromagnetic powder depending on the combination with the binder used. The range is 4 to 12, but
Preferably it is 6-10.

The ferromagnetic powder may be surface-treated with A2, Si, P, or oxides thereof. Its amount is 0.1-10% based on the ferromagnetic powder.

Soluble Na, Ca,
Although it may contain inorganic ions such as Fe and Ni5Sr, it does not particularly affect the characteristics if the amount is 500 ppm or less.

The ferromagnetic powder used in the present invention has Al in addition to the specified atoms.
, S i, S, Sc, Ti, V, Cr, CuXY, Mo
, Rh, Pd, Ag, Sn, Sb.

Te, W, Re5Au, Hg, Pb, Bt, La.

Ce, Pr5Nd, P, Co, Mn, Zn, Ni.

It may contain atoms such as Sr and B.

These ferromagnetic fine powders may be subjected to a conditioning treatment before dispersion using a dispersant, lubricant, surfactant, antistatic agent, etc., which will be described later.

Further, it is preferable that the ferromagnetic powder used in the present invention has fewer pores, and the value thereof is preferably 20% by volume or less, and more preferably 5% by volume or less.

The ferromagnetic powder used in the present invention can be manufactured according to a known method. As for the shape, it may be acicular, granular, rice grain, or plate-like as long as it satisfies the characteristics regarding the particle size shown above. When the magnetic properties of the magnetic recording medium of the present invention are measured in a magnetic field of 5 KOe, the squareness ratio of each layer is 0. It is preferably 6 or more, preferably 0.7 or more, more preferably 0.8 or more.

The thickness of the second layer is preferably 0.05μ to 0.8μ, particularly preferably 0.1 to 0.6μ. If it is less than about 0.05, the upper layer will be too thin and the electromagnetic conversion characteristics will be equal to those of the lower layer, which is not preferable. Furthermore, if the thickness exceeds about 0.8μ, no improvement in output in the long-lived wavelength region will be seen, which is undesirable.If the second layer is applied thinner than 0.8μ, conventional coating methods should be used, and the lower layer It is not impossible to apply so-called sequential layering, in which the material is coated, calendered, cured, and then coated again. However, from the viewpoint of cost, uniformity of thickness, etc.,
62, JP 62-124631, JP 62-212
It is preferable to carry out simultaneous multilayer coating as shown in JP-A No. 933, JP-A No. 62-214524, and the like.

The center line average surface roughness (hereinafter abbreviated as Ra) of the magnetic layer is preferably 4 μm or less with a cant off of 0.25 no, particularly 0.25 μm or less.
1 to 3 μm is preferable. If Ra is about 6 nm or more, contact between the magnetic layer and the head deteriorates, spacing loss increases, and output in a short wavelength region decreases, which is not preferable. In addition, there is an increase in modulation noise due to surface roughness.
/N decreases, which is not preferable. On the other hand, Ra is about 0.
If the thickness is less than 1 μm, the surface is too smooth, which increases the coefficient of friction of the magnetic recording medium and may deteriorate running performance, which is not preferable. The binder used in the present invention contains at least one of the following polar groups at 10-7 to 10-2 mol/
g containing a vinyl chloride copolymer and/or a polyurethane resin.

Polar group 000M, -3O,M, -0303M, PO
(OM)2, -NH,, OPO(OM)2 (M is hydrogen or an alkali metal) The above polar group-containing resin preferably contains at least 5% by weight of the total binder, particularly 10% by weight or more. preferable.

Polar groups other than those mentioned above are not necessarily effective in improving the dispersibility of iron oxide. The binder of the present invention may contain polar groups other than those mentioned above, such as OH groups and epoxy groups, together with the above polar groups.

If the polar group is less than about 10-7 mol/g, the dispersibility of the ferromagnetic powder will not be improved and it will be difficult to obtain a magnetic layer with a low Ra, which is the object of the present invention. On the other hand, if it exceeds about 10-3 mol/g, the polarity is too strong, which makes it difficult for the resin to dissolve in organic solvents, and the dispersibility of the ferromagnetic powder worsens, which is not preferable. The total amount of the binder including the hardening agent is preferably 15 to 30% by weight based on the ferromagnetic powder, especially 1
8 to 26% by weight is preferred.

If it is less than about 15%, the dispersibility of the ferromagnetic powder is insufficient, making it difficult to lower the Ra of the magnetic layer, and the durability of the magnetic layer decreases, which is not preferable.

If it exceeds about 30%, the magnetic flux density of the magnetic layer decreases and the output becomes low, which is not preferable.

Ra required for the magnetic recording medium of the present invention can be easily achieved by processing under the following calendar conditions.

Calendering is a process in which a raw material of a magnetic recording medium is heated between at least two rolls to smooth the surface. The hardness of the roll is preferably 30 degrees or more in Shore A, particularly preferably 60 degrees or more. If the hardness is less than about 30 degrees, it is difficult to obtain the surface roughness Ra of 0.5 to 4 μm required by the present invention, which is not preferable. Further, those having a hardness exceeding about 110 degrees are currently difficult to process into rolls, and are therefore not very preferable.

Preferably, the temperature between the calender rolls is 70 to 120°C, and the linear pressure is 200 to 500 kg/e1m. At temperatures below 70°C or below 200 kg/am, the surface of the magnetic layer will not become smooth;
If it is larger than kg/cm, the support will be easily deformed and the life of the roll will be shortened.Furthermore, the calender roll is preferably a combination of metal rolls.

Although the magnetic recording medium of the present invention can be used for magnetic recording with a shortest recording wavelength exceeding 0°8μ, it exhibits its original performance when used for magnetic recording with a shortest recording wavelength of 0.8μ or less. do. It is particularly preferable that the shortest recording wavelength is 0.5 μm or less.

Other embodiments are as follows.

In order to obtain better dispersibility and durability than the binders used in this invention, 000M, SO3M, 0303M, P=O
(OM)2, ○-P=O(OM)2, (M is a hydrogen atom or an alkali metal base), OH, NR"N"R'
(R is a hydrocarbon group) It is preferable to use one into which at least one polar group selected from epoxy group, 5H1CN, etc. is introduced by copolymerization or addition reaction. The amount of such polar groups is from 10-' to 10-3 mol/g, preferably from 10-' to 10-4 mol/g.

These binders have glass transition temperatures of 1100 to 150°C.
2 number average molecular weight 1.000 to 200,000, preferably 10.000 to 100,000, and a degree of polymerization of about 50 to 1.
．． It is about 000.

The structure of polyurethane resin is polyester polyurethane,
Known materials such as polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used.

Specific examples of these binders used in the present invention include VMCHlVAGF and VA manufactured by Union Carbide.
GD,VYES,,VYNC,VMCC,XYCC,X
YHL, XYSG, Kuchii Kagaku Kogyo Co., Ltd., MPR-TSN
, MPR-TMF, MPR-TM, manufactured by Denki Kagaku Co., Ltd., DX
80, DX81, DX82, DX83, Nippon Zeon MRIIO1MR100, 400X110A, Nippon PoI
Manufactured by J'7 Letang Co., Ltd., Ninoporan N2301, N2302
, N2304, Pandenx T-51 manufactured by Dainippon Ink Co., Ltd.
05, T-R3080, T5201, Harnosoku D-4
00, D-210-80, Chrisbon 6109.720
9. Toyobo U Byron R8200, UR8300,
RV530, RV280, Dainichiseika Chemical Co., Ltd., Diferamine 4020.5020.5100.5300.9020
．． 9022.7020, manufactured by Mitsubishi Chemical Corporation, MX5004,
Manufactured by Mitsubishi Kasei, Sunbren 5P-150, Asahi Kasei,
Examples include Saran F310 and F210.

The binder used in the present invention is used in an amount of 5 to 50 wt%, preferably 10 to 30 wt%, based on the ferromagnetic powder of each layer in both the first layer and the second layer. It is preferable to use a combination of 5 to 30 wt% when using vinyl chloride resin, 2 to 20 wt% when using polyurethane resin gold, and 2 to 2 Qwt% when polyisocyanate is used.

In the present invention, when polyurethane resin is used, the glass transition temperature is -50 to 100°C and the elongation at break is 100 to 2.
000%, the breaking stress is preferably 0.05 to 10 kg/cd, and the yield point is preferably 0.05 to 10 kg/cJ.

Examples of polyisocyanates used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, 0-toluidine diisocyanate, isophorone diisocyanate, and triphenyl diisocyanate. Isocyanates such as methane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates can be used. Commercially available product names of these isocyanates include Coronate, Coronate HL, and Coronate 2030 manufactured by Nippon Polyurethane Co., Ltd.
, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate ni-102, Takenate) D-11ON, Takenate D-200, Takenate D-200, Takenate D-202, Sumitomo Bayer, Desmodule, Death module IL, death module N1 death module HL.

These can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity for both the first layer and the second layer.

As the carbon black used in the present invention, furnace black for rubber, thermal black for rubber, black for color, acetylene black, etc. can be used.

Specific surface area is 5-500rrf/g, DBP oil absorption is 10
~40 (ld/100 g, particle size is 5 mμ ~ 300
mμ, pH is preferably 2 to 10, water content is preferably 0.1 to 10%, and tap density is preferably 0.1 to Ig/cc.

A specific example of carbon black used in the present invention is BLACKPEARLS 200 manufactured by Cabot Corporation.
0.1300.1000.900.800.700, V
ULCAN X C-72, manufactured by Asahi Carbon Co., Ltd., N80
, N60, N55, N50, N35, manufactured by Mitsubishi Chemical Industries, #240OB, #2300, #900, #1000.
#30, #40, #10B, manufactured by Conlonbia Carbon Co., Ltd., COMDIICTEX S C1RABVEN 15
Examples include 0.50, 40, 15, etc. Carbon black may be surface-treated with a dispersant, grafted with a resin, or a portion of the surface may be graphitized.

Further, carbon black may be dispersed in advance with a binder before being added to the magnetic paint.

These carbon blanks can be used alone or in combination. When carbon black is used, the amount relative to the ferromagnetic powder is 0. It is preferable to use it in an amount of 1 to 30 wt%.

Carbon black prevents static electricity in the magnetic layer, reduces the coefficient of friction,
It has functions such as imparting light-shielding properties and improving film strength, and these properties vary depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types and types in each layer.
Change the amount and combination, particle size, oil absorption, electrical conductivity, pH
Of course, it is possible to use them differently depending on the purpose based on the characteristics shown above.

For carbon blanks that can be used in the present invention, reference may be made to, for example, "Chikara - Bon Blank Handbook" Carbon Blank Association.

The abrasives used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide titanium carburide, and the like. Mainly Mohs 6, such as bits, titanium oxide, silicon dioxide, boron nitride, etc.
The above known materials may be used alone or in combination. Further, a composite of these abrasives (an abrasive whose surface is treated with another abrasive) may also be used. These abrasives may contain compounds or elements other than the main component, but as long as the main component is 90% or more, the effect remains the same. The particle size of these abrasives is preferably 0.01 to 2μ, but if necessary, abrasives with different particle sizes may be combined, or a single abrasive may be used with a wide particle size distribution to achieve the same effect. can. Tap density is 0.3~
2g/cc, moisture content 0. 1~5%, PH is 2~
11. The specific surface area is preferably 1 to 30 n(/g).

The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but it is preferable to have a part of the shape with a corner because of its high abrasiveness.

Specific examples of the abrasive used in the present invention include AKP-20, AK-30, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, manufactured by Nihon Kagaku Kogyo Co., Ltd., G5
, G7, s-i, manufactured by Toda Kogyo Co., Ltd., 100ED, 140E
D, etc.

After dispersing these abrasives with a binder,
It may be added to magnetic paint.

As the additives used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate ester, Alkali metal salts thereof, alkyl sulfate esters and their alkali metal salts, polyphenyl ethers, fluorine-containing alkyl sulfate esters and alkali metal salts thereof, -basic fatty acids with a carbon number of 10 to 24 (even if they contain unsaturated bonds, and branched ), and their metal salts (Li, Na, Cu, etc.)
Or monovalent, divalent, trivalent, tetravalent, having 12 to 22 carbon atoms,
Trihydric and hexahydric alcohols (which may contain unsaturated bonds or be branched), alkoxy alcohols with 12 to 22 carbon atoms, monobasic fatty acids with 10 to 24 carbon atoms (which may contain unsaturated bonds) (but may also be branched) and any one of monovalent, divalent, trivalent, tetravalent, trivalent, and hexavalent alcohols with 2 to 12 carbon atoms (even if they contain unsaturated bonds, monofatty acid ester, difatty acid ester, or trifatty acid ester consisting of (which may be branched), fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid ester having 8 to 22 carbon atoms, fatty acid ester having 8 to 22 carbon atoms, Fatty acid amines, etc. can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolic acid, elaidic acid, octyl stearate, amyl stearate,
Isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate,
Examples include anhydrosorbitan tristearate, oleyl alcohol, and lauryl alcohol.

In addition, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Cationic surfactants such as heterocycles, phosphoniums or sulfoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric ester groups, amino acids, amino sulfonic acids, etc. Ampholytic surfactants such as sulfuric acid or phosphoric acid esters of amino alcohols, alkylhedine type, etc. can also be used.

Regarding these surfactants, please refer to "Surfactant Handbook J
(published by Sangyo Tosho Co., Ltd.) is described in detail.

These lubricants, antistatic agents, etc. are not necessarily 100% pure and may contain isomers, unreacted substances, side reactants,
It does not matter if impurities such as decomposition products and oxides are included.

The content of these impurities is preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in different types and amounts in each layer as required.

In addition, all or part of the additives used in the present invention may be added at any step in the production of magnetic paint.
For example, when mixing with ferromagnetic powder before the kneading process, when adding during the kneading process of ferromagnetic powder, binder and solvent,
There are cases where it is added during the dispersion process, cases where it is added after dispersion, and cases where it is added just before coating.

Ari! used in the present invention! The solvent can be ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., alcohols such as methanol, ethanol, purpanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc. , esters such as methyl acetate, butyl acetate, isophthyl acetate, isopropyl acetate, ethyl lactate, ethyl acetate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, cresol, Aromatic hydrocarbons such as chlorobenzene, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorohenzene, NN-
Dimethylformamide, hexane, etc. can be used.

The thickness structure of the magnetic recording medium of the present invention is such that the nonmagnetic support has a thickness of 1 to 1.
100μ, preferably 6 to 20μ, and the first magnetic layer has a thickness of 0.
It is 5μ to 10μ, preferably 1 to 5μ. The total thickness of the magnetic layer is used in a range of 1/100 to 2 times the thickness of the nonmagnetic support.

Further, an intermediate layer such as an undercoat layer for improving adhesion or a layer containing carbon black for antistatic purposes may be provided between the nonmagnetic support and the second layer. The thickness of these is 0.01-2μ, preferably 0.05-0.5μ. Further, a back coat layer may be provided on the side of the nonmagnetic support opposite to the magnetic layer side. This thickness is 0.1~2
μ, preferably 0.3 to 1.0 μ. Known intermediate layers and back coat layers can be used.

The nonmagnetic support used in the present invention is a known film such as polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, etc. can be used. These supports may be subjected to corona discharge treatment, plasma treatment, adhesion treatment, heat treatment, dust removal treatment, etc. To achieve the object of the present invention, the nonmagnetic support should have a centerline average surface roughness of 0.03 μm or less, preferably 0.02 μm or less, and more preferably 0.03 μm or less.
It is preferable to use a material with a diameter of 0.01 μm or less. Furthermore, it is preferable that these nonmagnetic supports not only have a small center line average surface roughness, but also have no coarse protrusions of 1 μm or more. Furthermore, the surface roughness and shape can be freely controlled by the size and amount of filler added to the support as required. Examples of these fillers include oxides and carbonates of Ca, Si, and Ti, as well as organic fine powders such as acrylic powders.

The process of manufacturing the magnetic paint for the magnetic recording medium of the present invention includes at least a kneading process, a dispersion process, and a mixing process provided before or after these processes as necessary. Each individual process may be divided into two or more stages.

All raw materials used in the present invention, such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent, may be added at the beginning or middle of any step. In addition, individual raw materials may be added in portions in two or more steps. For example, polyurethane may be added in portions during a kneading process, a dispersion process, and a mixing process for adjusting the viscosity after dispersion.

In order to achieve the objectives of the present invention, conventional and well-known manufacturing techniques can be used as part of the steps. In the kneading step, it is preferable to use a kneader with strong kneading power, such as an open kneader, pressure kneader, or continuous kneader.

The method for coating a magnetic recording medium of the present invention is disclosed in Japanese Patent Application Laid-Open No. 62-21
A simultaneous multilayer coating method as shown in No. 2933 is used.

Further, for orientation, it is preferable to use a solenoid of 100 OG or more and a cobalt magnet of 200 parts or more in combination, and furthermore, it is preferable to provide an appropriate drying step in advance before orientation so that the orientation after drying is the highest.

(Effects of the Invention) The present invention includes a thin film of cobalt-containing iron oxide with high Hc in the upper layer, and a magnetic layer in the lower layer with an Hc of 0.8 times or less than that of the upper layer, and the Hc of the upper magnetic layer is 4 parts m or less. By making it extremely smooth, the output at long and short wavelengths is improved, and the C
/N could be improved. Good results can be obtained with such magnetic recording media, especially when a polar group-containing binder is used as the binder, and furthermore, by calendering at a predetermined Shore hardness at a predetermined temperature and linear pressure, the present invention can be achieved. An excellent magnetic recording medium was obtained.

(Example) Next, Examples and Comparative Examples will be shown to further specifically explain the present invention. In each case, "parts" means "parts by weight" unless otherwise specified.

Upper layer liquid (A liquid) Cor-r-FeOX 100 parts (x=1
．． 45, major axis length 0.20μ, Hc shown in Table 1) Vinyl chloride copolymer (containing 3.1X10-' mol/g of sulfonic acid groups) polyester polyurethane 5 parts (containing 1.25X10-' mol/g of sulfonic acid groups) /g) Polyisocyanate (Coronate L) 6 parts stearic acid (industrial use) 1 part butyl stearate (industrial use) 1 part α-alumina (particle size 0.1μ) 10 parts conductive carbon (particle size 7
0 mμ) 1 part methyl ethyl ketone/cyclohexynone = 7/3 solvent 200 Lower layer liquid (B
liquid) Cor-FeOX 100 parts (x=1
．． 45, major axis length 0.25μ, Hc shown in Table 1) Vinyl chloride copolymer 11 parts (containing 3.1X10-5 mol/g of sulfonic acid groups) Polyester polyurethane 4 parts (sulfonic acid groups 1.2
5 x 10-5 mol/g) polyisocyanate (Coronate L) 6 parts stearic acid (industrial)
1 part butyl stearate (industrial)
1 part conductive carbon black (particle size 20 mμ) 5
200 parts methyl ethyl ketone/cyclohexanone = 7/3 solvent 100 parts monolayer solution Cor-FeOX (x=1
．． 45, major axis length 0.25μ, Hc shown in Table 1) Vinyl chloride vinyl acetate copolymer 11 parts (contains 0.25% sulfonic acid group, made by Nippon Zeon: MR110) Polyester polyurethane 4 parts (sulfonic acid group (Contains 0.1%) Polyisocyanate 6 parts (Japan Polyurethane: Coronate L) Stearic acid (industrial use) 1 part Butyl stearate (industrial use) 1 part α-alumina (particle size 0.1μ)
10 parts Conductive carbon (particle size 70 mμ) 1
Part conductive carbon (particle size 20 mμ) 5 parts Methyl ethyl ketone/cyclo 200 parts Xanone = 7
/3 Solvent Simultaneous multi-layer and single-layer coating was performed using a coating solution prepared with the above composition. The support used was polyethylene terephthalate (PET) with an Ra of 4 nm and a thickness of 14 μm. After the above coating, the film was oriented in the longitudinal direction and dried by a known method to obtain a bulk roll. The obtained bulk roll was further subjected to calender roll treatment.

Calendar roll treatment has Shore A hardness of 80 degrees, Rag, 5
Seven layers of metal rolls in part m were stacked at a temperature of 80°C and a linear pressure of 300.
kg was processed. Example No. 8 achieved the desired Ra under the above conditions.
The process was repeated until . Also, comparative example C5
3 of the above rolls are made of nylon rolls (Situa A
The hardness was changed to 15 degrees and the Ra was 2 nm).

N010 is a vinyl acetate salt (Nissin Chemical type: MPR-) containing 0.7% by weight (2*10-5 mol/g) of carboxylic acid groups by replacing the sulfonic acid base with vinyl acetate salt as a binder in the lower layer. TM)
I did the same thing except I used . Comparative Example (-6) was carried out in the same manner except that vinyl acetate salt containing 2.3% by weight of hydroxyl groups (Nissin Chemical Type: MPPTA) was used as the binder for the upper and lower layers.

Comparative example (-8 is an axial length of 0.1 in place of the upper layer iron oxide magnetic material)
5μ metal ferromagnetic powder was used.

The Fe alloy magnetic material used in C-8 for the upper layer has a Hc of 2000
The characteristics of the tape obtained in the same manner as in the example of the present invention were as follows, except that a ferromagnetic material with an increased Oe and a ferromagnetic material with No. Shown in C-9.

Using the magnetic material used in NoC-8, JP-A-56-9
Similar to Example 3123, the characteristics of the tape obtained in the same manner as in the Example of the present invention except that the formulation of the upper and lower layers was changed as shown below.
-10.

Upper layer formulation Fe alloy ferromagnetic material 100 parts by weight Salt-vinylidene acetate copolymer 10 parts by weight Hat 1 ratio 1:L degree of polymerization 430) Vinylidene chloride copolymer 40 parts by weight (weight ratio 1:1) MEK-MI BK-Toluene 190 parts by weight Oleic acid 0.2 parts by weight Silicone oil 3 parts by weight Chromium oxide (Cr203
) 3 weight lower layer formulation 7-Fe2O3 magnetic powder 800 parts by weight BuA-
AN-2-HEMA 300 parts by weight-MA copolymer (weight ratio 5:1:I:l) 40 wL% MIBK solution MIBK 450 parts by weight Toluene 450 parts by weight VAGH (VC
-VAc- VOH copolymer) 75 parts by weight The resulting tape was measured and evaluated under the following conditions.

Measurement method Center line average surface roughness (Ra) Using a two-dimensional surface roughness meter (manufactured by Kosaka Institute), the surface of the magnetic layer was measured in the longitudinal direction with a cutoff of 0.25 [lll1l''?: The numerical value is small. This indicates that the roughness is small and the surface of the magnetic layer is smooth.

Output: A modified video deck NV-V 10000 manufactured by Matsushita Electric was used. C-7 metal tape was used as the reference tape.

The sine wave signals of each frequency shown in Table 1 were recorded at the optimum current for each signal (the current value at which the reproduction output is maximized). The average value of this reproduction output was measured with a level meter, and the ratio to the reference tape was expressed in decibels. The larger the number, the higher the output (
, indicating excellent recording characteristics at that recording wavelength.

C/N The reproduction output at each frequency shown in Table 1 was frequency analyzed, and the ratio between the output and the noise at I MHzRIi from each frequency was expressed in decibels. The larger the number, the greater the ratio of modulation noise to output at that frequency, indicating higher signal fidelity.

In addition, the reference tape (C-7) is 0.0d for both output and C/N.
This is a relative value to B.

The wavelength C (unit - μm) at each frequency (unit = H2) is shown below.

0.5MHz=11.6u, 2MHz=2.9μ, 8M
=0.13u, 12MHz=0.48μ, 15MHz=
0.39μ.

After applying calendar roll treatment to the above tape, 60°
The magnetic layer was cured by bulk thermolysis at C for 48 hours, and then slit into 1/2 inch width to obtain a videotape.

The obtained video tape was assembled into a VH5 type cassette to obtain a video cassette tape.

The obtained tape was used for measurement and evaluation under the following conditions.

Measurement method Center line average surface roughness (Ra) Using a three-dimensional surface roughness meter (manufactured by Kosaka Institute), the surface of the magnetic layer was measured in the longitudinal direction with a cutoff of 0.25 strokes. The smaller the value, the smaller the roughness and the smoother the surface of the magnetic layer.

Output: A modified video deck NV-V 10000 manufactured by Matsushita Electric was used. C-7 metal tape was used as the reference tape.

The sine wave signals of each frequency shown in Table 1 were recorded at the optimum current for each signal (the current value at which the reproduction output is maximized). The average value of this reproduction output was measured with a level meter, and the ratio to the reference tape was expressed in decibels. The larger the number, the higher the output, and the better the recording characteristics at that recording wavelength.

C/N The reproduction output at each frequency shown in Table 1 was frequency analyzed, and the ratio between the output and the noise at a distance of IMHz from each frequency was expressed in decibels.

The larger the number, the greater the ratio of modulation noise to output at that frequency, indicating higher signal fidelity.

In addition, the reference tape (C-7) is 0.0d for both output and C/N.
Relative value of B.

The wavelength (unit = μm) at each frequency (unit -Hz) is shown below.

0.5MHz=11.6μ, 2MHz=2°9μ, 8M
=0.73tt, 12MHz=0.48μ, 15MH2
=0.39u.

As shown in Table 1, the magnetic recording medium according to the present invention includes the conventional multilayer tape comparative example C-1, and the upper single layer comparative example (-7).
C/ in the ultra-short wavelength range from 12 MHz to 15 MHz compared to
It was found that this is preferable because of the high N content.

The Hc of the upper layer is approximately 1200 from the comparison of C-1 and Nos. 1 to 3.
It was found that 2000 Oe is preferable because of its high C/N. Moreover, it was found that a value of about 1400 or more is particularly preferable because the output becomes high.

The thickness of the upper layer is approximately 0.0 mm from a comparison between No. 2.4.5 and C-2.
It has been found that 1μ to 0.8 is preferable. In particular, 0.
If it is less than 6μ, the output in the long and medium wavelength range will be relatively high, which is preferable.

From a comparison of C-3, C-4, and No. 2.6.7, it was found that the lower layer Hc is preferably 0.9 times or less and 0.5 times or less than the upper layer.

If the Hc of the lower layer exceeds about 0.9 times that of the upper layer, the output in the long and medium wavelength range will decrease, which is not preferable.

Furthermore, if the Hc of the lower layer was less than 0.5 times that of the upper layer, the output at medium and short wavelengths would decrease, which was not preferable.

A comparison between No. 2.8.9 and C-5 revealed that Ra is preferably 4 μm or less.

If Ra exceeds 4 μm, it is not preferable because the output in the ultra-short wavelength region and the C/N decrease.

The object of the present invention was also achieved even when the type of polar group in vinyl chloride and vinyl acetate was changed from a sulfonic acid group to a carboxylic acid group. If the polar group of vinyl chloride or vinyl acetate was replaced with a hydroxyl group different from that of the present invention, the polarity would be low and the dispersibility of the ferromagnetic powder would be reduced, making it impossible to obtain the desired Ra and resulting in poor output and C/N, which was not preferred.

Further, a comparison with single-layer C7 revealed that the conventional magnetic tape using metal ferromagnetic powder had higher output but lower C/N and lower signal fidelity than the magnetic tape of the present invention.

Furthermore, in the conventionally known multilayer tape C9 having upper and lower Hc layers, the output at 6 MHz was unfavorable, perhaps because the difference in Hc between the upper and lower layers was too large.

Moreover, in the case of CIO which does not use the polar group of the present invention, the dispersibility is further significantly deteriorated, Ra increases, and the output and C/N decrease, so that it does not meet the purpose of the present invention.

From the above, the multilayer magnetic recording medium of the present invention has higher signal fidelity than the conventional metal magnetic recording medium, and also has higher output from the medium-long wavelength to ultra-short wavelength range than the conventionally known iron oxide multilayer magnetic recording medium. It turned out to be.

1.Display of the incident 2゜ name of invention 1991 2 Month 2-2 1990 Patent Application No. 233697 Magnetic recording medium and its manufacturing method Patent applicant: Fuji Photo Film Co., Ltd. 3゜ person who makes corrections Relationship with the incident address

Claims (3)

[Claims] (1) In a magnetic recording medium having at least two upper and lower magnetic layers in which ferromagnetic powder is dispersed in a binder on a non-magnetic support, the upper magnetic layer contains cobalt-containing iron oxide as ferromagnetic powder; The coercive force of the magnetic layer is 1200-200
0 Oe, and the dry thickness is 0.05 to 0.8μ, the lower magnetic layer contains cobalt-containing iron oxide as ferromagnetic powder, and the coercive force of the lower magnetic layer is equal to the coercive force of the upper magnetic layer. 0.8 times or less, the centerline average surface roughness (Ra) of the upper magnetic layer is 4 nm or less, and the shortest recording wavelength of the magnetic recording medium is 0.8 μ or less. magnetic recording medium. (2) The binder includes a vinyl chloride copolymer containing at least one of the following polar groups at 10^-^7 to 10^-^3 mol/g, and includes a curing agent. 2. The magnetic recording medium according to claim 1, wherein the total amount of is 15 to 30% by weight based on the ferromagnetic powder. Polar group: -COOM, -SO_3M, -OSO_3M,
-PO(OM)_2, -NH_2, -OPO(OM)_2 Here, M represents hydrogen, an alkali metal, or an ammonium salt. (3) Coat a magnetic paint in which cobalt-containing iron oxide and a binder are dispersed on a non-magnetic support to form at least two upper and lower magnetic layers, and after orientation and drying, the surface of the resulting magnetic layer has a Shore A hardness. Temperature 70 between calender rolls over 30 degrees
Calendar treatment at ~120°C and linear pressure of 200~500 kg/cm, and the coercive force of the upper magnetic layer is 1200~20
00 Oe and a dry thickness of 0.05 to 0.8μ, the magnetic recording medium is characterized in that the coercive force of the lower magnetic layer is 0.8 times or less than the coercive force of the upper magnetic layer. Production method.