JPH0467428A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and travel durability and to lessen an increase in DO by providing >=2 layers of magnetic layers contg. carbon blacks and forming the 1st magnetic layer (lower layer) into >=100 to 150ml/100g DBP oil absorption of the carbon blacks and the 2nd magnetic layer (upper layer) into <=80ml/100g. CONSTITUTION:The magnetic layers contg. ferromagnetic powder, binder and the carbon blacks are provided in >=2 layers on the surface of a nonmagnetic base. The DBP oil absorption of the carbon black contained in the 1st magnetic layer (lower layer) is >=100 to 150ml/100g and the DBP oil absorption of the carbon black contained in the 2nd magnetic layer (upper layer) is <=80ml/100g. Therefore as a whole of the magnetic layers, the electromagnetic conversion characteristics and increase in DO are improved by the 1st magnetic layer having excellent smoothness and electrical conductivity and the traveling durability and electromagnetic conversion characteristics are improved by the 2nd magnetic layer. The electromagnetic conversion characteristics and traveling durability are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic recording medium, and more particularly to an improvement in a magnetic recording medium having at least two magnetic layers.

In particular, the present invention relates to a magnetic recording medium with improved runnability, durability, increased D○ (dropout), and tVA conversion characteristics.

(Prior Art) Magnetic recording media in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support are generally used as magnetic recording media for audio, video, or computers. ing. Audio tapes and video tapes are increasingly being used with cassettes attached.

Usually, the magnetic layer of such a magnetic recording medium contains carbon black for the main purpose of preventing static electricity. The average particle size of commonly used carbon bras is 10
~150 μm.

- For boat fishing, if a carbon blank with a small particle size is used, the surface of the resulting magnetic layer will be smooth, but it will be inferior in terms of running durability and heat resistance. On the other hand, if the particle size of carbon black is large, the running durability and heat resistance are good, but the smoothness is poor, so that the electromagnetic conversion characteristics, especially in the case of video tape, the S/N becomes small, which is not preferable.

For this reason, attempts were made to incorporate carbon blanks in various combinations of average particle diameters into the magnetic layer in a single-layer system (Japanese Patent Publication No. 9041/1983, Japanese Patent Publication No. 53/1983). Publication No. 20203, JP-A-58-218
No. 039 (disclosed in Japanese Patent Publication No. 039), however, it was not possible to obtain a product that satisfied both running durability, heat resistance, and electromagnetic conversion characteristics.

Also, in Japanese Patent Application Laid-Open No. 61-55727, S-A is 15rr.
r/g or more and less than 50r+(/g, and a DBP oil absorption of 200d/100g or less, and Ss!t of 900 bi/g or more and a DBP oil absorption of 200d/100g or more. It has been proposed to include a certain second carbon blank in the magnetic layer, and also in JP-A-63-
Publication No. 253530 includes SIl! A is 50 g/g or more9
00bo/g or less, DBP oil absorption is 110atff
a first carbon blank having a weight of less than i/100g;
IET is 15 po/g or more and 80 bo/g or less, and D
It has been proposed to use a combination of a second carbon black with a BP oil absorption of 110 d/100 g or more in the magnetic layer. However, it had the following drawbacks.

That is, it was not possible to simultaneously improve surface electrical resistance, video S/N, increase in drop-out, and running durability.

In addition, in the case of a multilayer system with two or more magnetic layers, it is known that the electromagnetic conversion characteristics can be improved by making the upper magnetic layer thinner. The effect of the amount of non-magnetic powder added and the particle size is greater than that of conventional single layer, making it difficult to achieve both runnability, durability, and electromagnetic conversion characteristics. In the case of multilayer system, JP-A-58-20
Publication No. 0425, JP-A No. 63-300425, JP-A-1
205726, etc., but at present, magnetic recording media based only on various specifications of the average-order particle system have not been able to provide sufficiently excellent durability and increase in Do.

(Objective of the Invention) An object of the present invention is to provide a magnetic recording medium that has at least two magnetic layers and has good electromagnetic conversion characteristics, running durability, and little increase in DO.

(Structure of the Invention) The above object of the present invention is to provide a magnetic recording medium in which at least two or more magnetic layers containing ferromagnetic powder, a binder, and a carbon blank are provided on the surface of a non-magnetic support. The DBP oil absorption amount of the carbon black contained in is 1
00 to 15t) d/100g or more, and the second magnetic layer (
This can be achieved by a magnetic recording medium characterized in that the carbon black contained in the upper layer has a DBP oil absorption of 80-/100 g or less.

More preferably, the above object of the present invention is such that the carbon blank contained in the first magnetic layer is 1.0 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder, and the carbon black contained in the second magnetic layer is is 0 for the ferromagnetic powder.
．． This can be achieved by a magnetic recording medium characterized in that the amount is 1-10 parts by weight. More preferably, the binder for the first magnetic layer includes a vinyl chloride copolymer having a polar group and a polyurethane resin having no polar group, and the binder for the second magnetic layer includes a vinyl chloride copolymer having a polar group. containing a copolymer and a polyurethane resin having a polar group, and the polar group is an epoxy group, COOM, SO3M, 0503 M,
This can be achieved by a magnetic recording medium characterized in that M is a polar group of hydrogen, an alkali metal, or ammonium in at least one member selected from PO2Mx, -0PO,M.

The DBP oil absorption amount of the carbon black of the present invention was defined by the following measuring method.

Add DBP (Dibut) to 100g of carbon blank.
ylphthalate) little by little, observed the state of the carbon black while kneading it, and found the point where it formed a single lump from a dispersed state.DB
Let the d number of P be the DBP oil absorption amount.

The present invention is a magnetic recording medium having a basic structure in which a first magnetic layer and a second magnetic layer are provided in this order on the surface of a nonmagnetic support.

The first magnetic layer of the present invention has a DBP oil absorption of 100d-15
0d carbon black as ferromagnetic powder in the magnetic layer
The second magnetic layer contains carbon black having a DBP oil absorption of 80 d or less in an amount of 100 parts by weight of ferromagnetic powder in the magnetic layer. There is.

That is, the first magnetic layer of the magnetic recording medium of the present invention contains carbon black with a high DBP oil absorption that relatively easily forms a strutted structure, so that high conductivity can be obtained. Furthermore, since the dispersibility is low, the surface of the magnetic layer can have extremely good smoothness.

The reason why carbon blanks with high DBP oil absorption have excellent electrical conductivity is that the carbon blanks with high DBP absorption/113 have primary particles of carbon black connected in a grape-like manner (with developed struttles), which makes them electrically conductive. This is because the resistance becomes lower and the conductivity becomes higher.

In addition, the reason for the excellent smoothness is that the carbon blank particles are less likely to agglomerate due to the high stracture structure.In other words, the primary particles of the carbon blank are connected, which prevents the secondary particles from coagulating with each other. , large aggregation of carbon black is eliminated, dispersibility is improved, and the surface of the magnetic layer has excellent smoothness.

On the other hand, in the second magnetic layer of the present invention, by using carbon black having a relatively low DBP oil absorption, the coefficient of friction can be reduced with the addition of a small amount, and the running stability can be improved as described above. Moreover, since it is added in a small amount, the degree of filling of the ferromagnetic powder can be improved, and the electromagnetic conversion characteristics can be improved.

The reason why DBP with low oil absorption can lower the coefficient of friction is that because the primary particles of the carbon blank have relatively few connections, carbon black itself tends to appear on the surface, and the moderate unevenness of carbon black and carbon black This is because the effect of its own slipperiness can be fully exhibited.

Therefore, as for the magnetic layer as a whole, the first magnetic layer with excellent conductivity and smoothness has excellent electromagnetic conversion characteristics and DO increase, and the second magnetic layer has excellent running durability and electromagnetic conversion characteristics. A magnetic recording medium having the above structure can have excellent electromagnetic conversion characteristics and running durability.

In order to obtain the above-mentioned excellent magnetic conversion characteristics, it is advantageous for the second magnetic layer to be thinner.

On the other hand, in order to obtain sufficient conductivity, the thicker the layer, the more advantageous it is.

Specifically, the thickness of the second magnetic layer is preferably in the range of 0.1 to 1.5 μm in order to obtain both of the above characteristics. Further, in order to obtain smoothness of the surface of the magnetic layer, it is advantageous for the first magnetic layer to be thicker, and preferably has a thickness of 2.8 μm or more.

The content of carbon blank in each magnetic layer of the present invention is determined from the viewpoint of ensuring the light-shielding property of the first magnetic layer.
1.00 parts by weight. It is contained within the range of 0 to 20 parts by weight, preferably 3 to 15 parts by weight. 1. If it is less than 0 parts by weight, the light shielding property will not be sufficient, and if it exceeds 20 parts by weight, the degree of filling of the ferromagnetic powder will be low, which is not preferable.

From the viewpoint of ensuring conductivity, the second magnetic layer is made of 0.00% by weight based on 100 parts by weight of the ferromagnetic powder in the magnetic layer. It is contained within the range of 1 to 10.0 parts by weight, preferably 0.1 to 8.0 parts by weight. If it is less than 0.1 parts by weight, the running durability will be reduced, and if it exceeds 10 parts by weight, the degree of filling of the ferromagnetic powder will be low and the t-magnetic conversion characteristics will be deteriorated, which is not preferable.

The carbon black used in the above two magnetic layers is
It is not particularly limited as long as it has the above oil absorption amount.

An example of a product name for a carbon bra with oil absorption of 80 iF/100 g is RAVEN.

1085, Lehen 850 (manufactured by Columbia Carbon), Asahi #50 (manufactured by Asahi Carbon), suction amount 100-1
Examples of product names for 50 frog/100 g carbon blanks are Asahi #60H (manufactured by Asahi Carbon ■), Lehen 1
6 (manufactured by Columbia Carbon).

These are only examples of specific commercial products of carbon black, and any carbon black that satisfies the above-mentioned oil absorption conditions can be used.

Moreover, there is no problem even if these are used in combination.

The ratio of the magnetic powder to the binder contained in the first magnetic layer and the second magnetic layer of the present invention is such that the magnetic powder/binder is 2.
．． 5 to 10.0, and the difference in the ratio between the first magnetic layer and the second magnetic layer is 5 or less.

The magnetic recording medium of the present invention can be manufactured, for example, as follows.

Non-magnetic supports used in the present invention include polyethylene terephthalate (PET), polyesters of polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyvinyl chloride, polyvinylidene chloride, etc. films or sheets made of synthetic resins such as vinyl resin, polycarbonate, polyamide, polyamideimide, polyimide; non-magnetic metal foils such as aluminum and copper; metal foils such as stainless steel foils; paper, ceramic sheets, etc. The thickness of the non-magnetic support is generally 2.5 to 100 μm, preferably 3 to 80 μm.
It is μm.

The magnetic layer in the magnetic recording medium of the present invention is a layer in which ferromagnetic powder is dispersed in a binder. There are no particular limitations on the magnetic powder used in the present invention. An example is y-F
e, O,, FeOx (1°33<x<1.5), Co
containing yFezos, Co containing FeOx (1,33
<x<1.5), Fe, O, Co-containing Fe, 04
, Cr0z, Co-N1-P alloy, Fe-Co-Ni alloy, and other known ferromagnetic powders.

The magnetic recording medium of the present invention has a multilayer magnetic layer consisting of a first magnetic layer and a second magnetic layer, each of which has different characteristics. That is, the first magnetic layer is designed to have as large a residual magnetization as possible, mainly in order to provide excellent reproduction output at long wavelengths. For this purpose, the average particle diameter of the ferromagnetic powder is preferably 5 Onf/g or less, more preferably 40 rrf/g or less, based on the BJ and T method specific surface areas. The crystallite size is preferably 210 Å or more.

In addition, the characteristics required of the second magnetic layer include electromagnetic conversion characteristics, especially large playback output for short wavelength recording, and high S/S/
It is N. For this purpose, it is necessary to use the above-mentioned ferromagnetic powder with a small average particle size, and the particle size of such ferromagnetic powder is 30rI? according to the BET method specific surface area. /g or more is preferable. And the crystallite size is 350
Å or less is preferable. Particularly preferred among such ferromagnetic powders is cobalt-modified 7 FezO3, in which the coercive force of the ferromagnetic powder contained in the second magnetic layer is 10,000e or less, and the coercive force of the ferromagnetic powder contained in the second magnetic layer is 10000e or less, and The coercive force of the ferromagnetic powder is 6000e or more. In the case of such a combination, extremely excellent electromagnetic conversion characteristics can be obtained, and the effect of using the carbon blank of the present invention becomes remarkable.

The binder solution for producing the magnetic paint used in the present invention is a binder solution containing a resin component, a solvent, and, if necessary, an abrasive, a lubricant, and the like.

The resin component is a conventionally known thermosetting resin, thermosetting resin,
Alternatively, reactive resins or mixtures thereof are used. Examples of resin components include vinyl chloride copolymers (e.g., vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinyl acetate copolymers,
Vinyl alcohol copolymer, vinyl chloride, vinyl acetate,
Acrylic acid copolymer, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/acrylonitrile copolymer, ethylene/vinyl acetate copolymer, -8○, M -03O,M
, P Os Mz , OP Ox Mz teM is hydrogen,
vinyl chloride copolymers into which polar groups such as alkali metals and ammonium and/or epoxy groups have been introduced), cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acecool resins, polyvinyl butyral resins, epoxy resins, phenoxy resins, Polyurethane resin (e.g. polyester polyurethane resin, -503M
-0303M, P03M2, -0P03M2, in which M is hydrogen, an alkali metal, or a polar group such as ammonium is introduced, such as polyurethane resins and polycarbonate polyurethane resins).

In the present invention, the binder for the first magnetic layer includes a vinyl chloride copolymer having a polar group and a polyurethane resin having no polar group, and the binder for the second magnetic layer includes a vinyl chloride copolymer having a polar group. It is particularly preferable to use a copolymer and a polyurethane resin having a polar group. This is because in the first magnetic layer, the carbon blank with a relatively large DBP oil absorption is connected in a grape shape and has a developed stracture structure, so it has good dispersibility and high conductivity, and it also has polar groups. Sufficient dispersion can be achieved by using a vinyl chloride copolymer, and polyurethane with low Tg (glass transition temperature), good moldability, and no polar groups can be used, and it has extremely excellent surface properties. A magnetic recording medium can be obtained.

Since the second magnetic layer contains a highly conductive carbon blank in the first magnetic layer, only a small amount is required, the μ value is reduced, and the electromagnetic conversion characteristics are also improved. Since the DBP oil absorption is relatively small, the dispersibility is slightly lowered, but excellent effects were obtained by including polar groups in both the vinyl chloride copolymer and the polyurethane resin.

Furthermore, when a curing agent is used, a polyisocyanate compound is usually used. The polyisocyanate compound is selected from those commonly used as a curing component of polyurethane resins and the like.

In addition, when performing curing treatment by electron beam irradiation, compounds with reactive double bonds (e.g. urethane acrylate)
Can be used for days.

Further, it is preferable to use an abrasive material in the magnetic layer of the present invention for the purpose of improving the running durability described above.

The abrasive used in the present invention preferably has a Mohs hardness of 5 or more. For example, MgO (Mohs hardness 6), Cr
z 03 (Mohs hardness 8.5), αAlz 03
(Mohs hardness 9), r-An, 03 (Mohs hardness 7~
8), SiC (α or β, Mohs hardness 9.5), a
Examples include Few O3, BN, silicon nitride, iron nitride, corundum, artificial corundum, diamond, garnet, and the like. Among these, α-A 1 z O* is preferred.

The average particle size generally ranges from 0.05 to 1.0 μm, preferably from 0.10 to 0.50 μm. The content of the abrasive is 0.1 to 12 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the magnetic particles. 0
．． If it is less than 1 part by weight, running durability will not be sufficient, and if it exceeds 12 parts by weight, electromagnetic conversion characteristics will deteriorate and head wear will increase, which is not preferable. If necessary, particles of different types, particle diameters, and/or materials may be mixed and used.

The abrasive material is preferably used in the second magnetic layer,
It is preferable not to use it in the first magnetic layer in order to prevent a decrease in magnetic flux density and deterioration of surface smoothness.

Examples of solvents used in the production of magnetic paints include ketones such as acetone, methyl ethyl getone, methyl isobutyl ketone, ethyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, and acetic acid glycol monoethyl ether. Glycol ethers such as ether, glycol dimethyl ether and dioxane; Aromatic hydrocarbons such as Hensen, toluene and xylene; Methylene chloride, ethylene chloride,
Chlorinated hydrocarbons such as tetracarbon L chloroform, ethylene chlorohydrin, and dichlorobenzene can be used, and these solvents can be used alone or in combination. Particularly preferred are polar solvents such as ketones or solvents containing polar solvents.

When producing magnetic paint, magnetic powder is uniformly kneaded and dispersed together with a binder solution. For this kneading and dispersion, a method is generally used in which pre-dispersion is performed using a two-roll mill, three-roll mill, open kneader 5 pressurized kneader, continuous kneader, etc., and then post-dispersion is performed using a sand grinder ball mill or the like.

In magnetic paint, lubricants, dispersants,
Of course, any one of various additives such as these may be added depending on the purpose.

For coating, a magnetic paint prepared from the above materials is applied onto a non-magnetic support by the following method. First, a coating liquid for the first magnetic layer is prepared by cross-dispersing magnetic layer forming components such as a resin component for the first magnetic layer, a ferromagnetic powder, and a curing agent blended as desired with a solvent. A coating liquid for the second magnetic layer is also prepared in the same manner as for the first magnetic layer.

The method for producing a magnetic recording medium of the present invention includes, for example, applying a coating solution for a first magnetic layer onto the surface of a non-magnetic support while it is running, so that the thickness of the first magnetic layer after drying is preferably 3 μm or more. (particularly preferably within the range of 3 to 5 μm), and while the coated layer is in a wet state, the coating liquid for the second magnetic layer is continuously applied to the coated layer to the thickness of the second magnetic layer after drying. is 1.5μm
It is preferable to apply the coating to the following thickness (more preferably 0.1 to 1.0 μm). The method of continuously coating these two layers is, for example, when using an extrusion coater as a coating machine.
It is also possible to apply two pressure coats in succession so as to sandwich the non-magnetic support while it is running, or the first magnetic layer is wet (that is, the coated layer still contains solvent and is sticky). It is also possible to install two units with an interval between them within a range that can maintain the condition (indicating 1).

Applicators for applying the above magnetic paint include air doctor coat, flade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, Spray coat, spin cord, etc. can be used. In the present invention, an extruder for simultaneous multilayer coating having two slots as shown in JP-A-62-124631 is particularly desirable.

The second magnetic layer obtained by using the above manufacturing method has a uniform layer thickness even if it is an extremely thin magnetic layer of 1.5 μm or less, and is coated with an extremely smooth surface. be able to.

Thereby, it is possible to manufacture the magnetic recording medium of the present invention which has excellent running durability and does not impair electromagnetic conversion characteristics.

A hack layer (backing layer) may be provided on the surface of the nonmagnetic support used in the present invention that is not coated with the magnetic paint. Usually, a hack layer is formed by applying a bank layer-forming paint consisting of particulate components such as abrasives and antistatic agents and a binder dispersed in an organic solvent to the surface of a non-magnetic support that is not coated with magnetic paint. It is a layer provided.

Note that an adhesive sublayer may be provided on the surface of the nonmagnetic support on which the magnetic paint and the hack layer-forming paint are applied.

Usually, the coated layer of magnetic paint is dried after being subjected to a treatment for orienting the ferromagnetic powder contained in the coated layer of magnetic paint, that is, a magnetic field orientation treatment.

After being dried in this manner, the coated layer is subjected to surface smoothing treatment. For example, a super calender roll is used for the surface smoothing process. By performing the surface smoothing treatment, the pores created by the removal of the solvent during drying are eliminated and the filling rate of the ferromagnetic powder in the magnetic layer is improved, making it possible to obtain a magnetic recording medium with high electromagnetic conversion characteristics. can.

The thus cured laminate is then cut into a desired shape.

The cutting can be carried out under normal conditions using a normal cutting machine such as a slitter.

Although the magnetic recording medium of the present invention has been described as having an upper and lower two-layer system, it may have three or more layers as a whole as long as it maintains the above specified properties and includes two magnetic layers.

(Effects of the Invention) The first magnetic layer of the magnetic recording medium of the present invention has a DBP oil absorption of 100i to 100i, which has a high DBP oil absorption and is relatively easy to take a strutted structure.
150#li! Because it contains carbon bra,
High conductivity can be obtained, and since the dispersibility is excellent, the magnetic layer can have extremely good surface smoothness.

On the other hand, the second magnetic layer of the present invention contains 80d carbon black, which has a low DBP oil absorption and is relatively difficult to form a stracture structure, so the friction coefficient can be reduced by adding a small amount, ensuring running stability of the medium. It is possible to increase the filling degree of the magnetic layer by adding a small amount.

Therefore, the magnetic layer as a whole has excellent electromagnetic conversion characteristics and Do increase due to the first magnetic layer having excellent smoothness and conductivity.
Since the second magnetic layer provides excellent running durability and ii[i conversion characteristics, it can be said that the magnetic recording medium having the structure of the present invention is excellent in both electromagnetic conversion characteristics and running durability.

In addition, the first magnetic layer contains a vinyl chloride copolymer having a polar group with good dispersibility, a polyurethane resin having no polar groups with good moldability, and a relatively high oil absorption amount that provides good dispersibility and conductivity. By combining carbon black with a large carbon black, a magnetic recording medium with good moldability and a high degree of filling can be obtained.

By using the above-mentioned carbon blank with a relatively small DBP oil absorption in the second magnetic layer and using a combination of a vinyl chloride copolymer having polar groups and a polyurethane resin having granular groups, it is possible to disperse the DBP evenly and in trace amounts. Addition of carbon black effectively reduces the coefficient of friction. And the degree of filling of the magnetic layer is improved.

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

[Example 1] -' Cor-r-Fe, off 100 parts [
)1c: 6500e, crystallite size S BET
Specific surface area, 35 Bi/g) Binder A Binder B Carbon black butyl stearate Stearate butyl acetate 2゛Co-7-Fezo3 [Hc: 7000e, crystallite size: S BET
Specific surface area = 40 bo/g] Binder A Binder B Carbon black α-A2□03 (Average particle size: 0.6 μm) Butyl stearate Stearate Butyl acetate 330 people Listed in Table 1 Listed in Table 1 Listed in 1 table 1 part 2 parts 200 parts 100 parts 300 people.

Listed in Table 1 Listed in Table 1 Listed in Table 1 6 parts 1 part 2 parts 200 parts For each of the above two paints, each component was kneaded and dispersed using a sand mill. 6 parts of polyisocyanate and 40 parts of butyl acetate were added to the obtained dispersion and filtered using a filter having an average pore size of 1 μm to prepare coating solutions for forming the first magnetic layer and for forming the second magnetic layer, respectively. did.

The coating liquid for forming the first and second magnetic layers is applied in the first step.
The following procedure was carried out using an extrusion coat for simultaneous multilayering having a slot for applying a magnetic layer and a slot for applying a second magnetic layer.

The obtained coating liquid for the first magnetic layer has a thickness of 3.5 mm after drying.
While running a polyethylene terephthalate support with a thickness of 14 μm at a speed of 60 m/min,
Coat the surface of the support using an extrusion coater having slots for coating the second magnetic layer, and immediately thereafter (while the first magnetic layer is still wet) apply the coating solution for the second magnetic layer to the thickness after drying. is 0
．． The second magnetic layer is coated to a thickness of 5 μm using an extrusion coater having a slot for coating, and while the magnetic layer is wet, it is oriented using the above magnet, and after drying, supercalendering is performed to form a 1/2 inch width. was slit to produce videotape.

/ / Regarding the video tapes obtained in the above examples, the composition of the magnetic layer is shown in Table 1, and the physical properties of each tape measured by the following measuring method are shown in Table 1.

Isashi method (1) Surface electrical resistance It was measured using a digital surface electrical resistance meter: TR-8021A, manufactured by Takeda Riken ■. The measurement conditions are temperature 2
3°C,'IL degree 30%RH and sample size 1
/2 inch x 1/2 inch.

(2) Video S/N Using a noise meter (925C, manufactured by Shibaku),
/N, and use the reference tape as 5upper AG T12.
0 (manufactured by Fuji Photo Film@) and the difference in S/N was determined. The noise level was measured using a bypass filter of 10 kHz and a low bass filter of 4 MHz. The VTR used was NV-8300 [manufactured by Matsushita Electric Industrial ■].

(3) Increase in dropouts The number of dropouts after running the T-120 tape repeatedly for 100 passes is shown.

Dropout is 15x1 with dropout counter
The number of 15 minutes in which the reproduction output decreased by 16 dB or more in a period of 0-'sec or more was displayed.

(4) Running durability A T-120 videotape was run on a VH3 type VTR under the conditions of 40°C and 180% RH, and a full-length running test was conducted repeatedly. It is expressed as the number of times the vehicle runs until it no longer appears.

The following can be seen from the 1st m-th result.

In other words, samples NCL2-4.6-8.10-26 of the present invention, in which the DBP oil absorption amount of carbon black contained in the first magnetic layer and the second magnetic layer are in a fixed relationship, have a video S/N.
It shows good results in terms of increased number of dropouts and number of passes of running durability. Here the video S/N is +0.3d
B or higher is a practical level, and the increase in the number of dropouts is 7
0 or less is a practical level, and the number of passes for running durability is 2.
50 or more is a practical level. Sample No. 1.5.9, which was outside the scope of the present invention, did not give good results in the above characteristics.

Preferred embodiments of the magnetic recording medium of the present invention are as follows.

(1) The first magnetic layer contains 3.0 parts by weight of the above carbon black based on 100 parts by weight of the ferromagnetic powder. The above-mentioned magnetic recording medium, characterized in that it contains within the range of 0 to 15 parts by weight.

(2) The magnetic recording medium described above, wherein the second magnetic layer contains the carbon blank in an amount of 0.1 to 8.0 parts by weight based on 100 parts by weight of the ferromagnetic powder.

(3) The magnetic recording medium described above, wherein the first magnetic layer has a thickness of 2.8 μm or more, and the second magnetic layer has a thickness of 1.5 μm or less.

(4) The BET specific surface area of the ferromagnetic powder contained in the first magnetic layer is 40rrf/g or less and the crystallite size is 210.
1 angstrom or more, the BET specific surface area of the ferromagnetic layer powder contained in the second magnetic layer is 30 rd/g or more, and the crystallite size is 350 angstrom or less.

(5) The second magnetic layer contains an abrasive material with a Mohs hardness of 7 or more in a range of 0.1 to 15 parts by weight per 100 parts by weight of ferromagnetic powder, and the first magnetic layer contains substantially no abrasive material. The above-mentioned magnetic recording medium is characterized in that it does not contain.

(6) 'F'Cf of ferromagnetic layer powder contained in the second magnetic layer
a force is 10000e or less, the coercive force of the ferromagnetic powder contained in the first magnetic layer is 6000e or more, and the ferromagnetic powder contained in the first magnetic layer and the second magnetic layer is cobalt-modified γ- Fe20. The above magnetic recording medium characterized in that:

Claims (2)

[Claims] (1) DBP oil absorption of the carbon black contained in the first magnetic layer (lower layer) in a magnetic recording medium in which at least two or more magnetic layers containing ferromagnetic powder, a binder, and carbon black are provided on the surface of a nonmagnetic support. The amount is 100-150m
l/100g or more, and the DBP oil absorption amount of the carbon black contained in the second magnetic layer (upper layer) is 80ml/1
A magnetic recording medium characterized by having a weight of 00g or less. (2) The carbon black contained in the first magnetic layer is 1.0 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder, and the carbon black contained in the second magnetic layer is contained in the ferromagnetic powder. The magnetic recording medium according to claim 1, wherein the amount is 0.1 to 10 parts by weight. (3) The binder for the first magnetic layer includes a vinyl chloride copolymer having a polar group and a polyurethane resin having no polar group, and the binder for the second magnetic layer includes a vinyl chloride copolymer having a polar group. Contains a polyurethane resin having a polymer and a polar group, and the polar group is an epoxy group, COOM, -SO_3M, -OS
Claims (
1) Magnetic recording medium.