JPH05298673A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a head clog characteristic and to prevent the degradation in output at a low temp. by incorporating conductive fine powder into the magnetic layer of the uppermost layer on a nonmagnetic supporting base and incorporating nonmagnetic powder of high permeability material into one layer exclusive of the uppermost layer. CONSTITUTION:The plural layers are formed on the nonmagnetic supporting base. The magnetic layer 2 of the uppermost layer is formed to <=0.8mum film thickness and is formed by incorporating carbon black having 40 to 120nm average grain sizes as the conductive fine powder therein at 0.1 to 1.0 pts.wt. per 100 pts.wt. magnetic powder. The intermediate layer 4 exclusive of the uppermost layer contains the nonmagnetic powder or the high permeability powder and its average grain size is selected at 1 to 50nm. The surface of the magnetic layer of the uppermost layer can be controlled by providing the uppermost layer and regulating the amt. of the conductive fine powder of the upper and lower layers while the layer 4 is in a moist state. Then, the good head clog at 0 deg.C is obtd. and the generation of the degradation in the output at and under 40 deg.C and 20% RH is obviated while good CN ratio and overwriting characteristic are maintained. The provision of a back coat layer 3 is effective for improving the traveling property of the medium and preventing electrification and transfer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium that is excellent in head clog characteristics at low temperatures and in output reduction prevention under low humidity.

[0002]

BACKGROUND OF THE INVENTION JP-A-63-259826 and JP-A-3
No. 119516 discloses a magnetic recording medium in which the amount of carbon in the upper and lower layers is specified. However, in both cases, the magnetic layer is used as the lower layer, and the thickness of the uppermost magnetic layer is relatively large, so that the thickness loss and the self-demagnetization loss are large, and they are unsuitable as a digital recording medium. Particularly in JP-A-63-259826, the lower layer is dried,
Wet on dr to apply upper layer after calendering
Since the y method is used, it is difficult to reduce the thickness of the upper layer.
This point can be improved by providing a layer containing a non-magnetic powder or a material having a high magnetic susceptibility as the lower layer and setting the thickness of the uppermost layer to 0.8 μm or less, preferably less than 0.5 μm. Since a smooth surface is required, the head clog characteristics deteriorate at low temperature (0 ° C) or under low humidity (40 ° C,
It was found by the study of the present inventor that output reduction occurs at 20% RH).

[0003]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic recording medium which is excellent in head clog characteristics at low temperatures and in output reduction prevention under low humidity.

[0004]

The magnetic recording medium according to the present invention for achieving the above object comprises a plurality of layers formed on a non-magnetic support, and the thickness of the uppermost magnetic layer is 0.8 μm. The conductive fine powder is the magnetic powder 100 in the uppermost magnetic layer.
0.1 to 1.0 parts by weight with respect to parts by weight, at least one layer other than the uppermost layer is a layer containing non-magnetic powder or high magnetic permeability material, 100 parts by weight non-magnetic powder or high magnetic permeability material The conductive fine powder is contained in an amount of less than 1.0 part by weight per part.

[0005]

In the present invention, in order to solve the above problems, a plurality of layers are formed on a non-magnetic support, and the thickness of the uppermost magnetic layer is 0.8 μm or less. Conductive fine powder is contained in the upper magnetic layer in an amount of 0.1 per 100 parts by weight of magnetic powder.
To 1.0 part by weight, and at least one layer other than the uppermost layer is a layer containing a non-magnetic powder or a high-permeability material. It is necessary that the powder be contained in less than 1.0 part by weight.

The conductive fine powder contained in the uppermost layer is 0.1 to 1.0 part by weight of the magnetic powder, more preferably 0.1.
~ 0.5 parts by weight. The conductive fine powder used has an average particle diameter of usually 10 to 300 nm, preferably 30 to 150 nm, more preferably 40 to 120 nm.
Is. The conductive fine powder contained in at least one layer other than the uppermost layer is less than 1.0 part by weight, more preferably 0.4 part by weight or less. The average particle size of the conductive fine powder used in the layer is usually 10 to 300 nm,
Preferably 10-150 nm, more preferably 10-1
It is 20 nm.

The conductive fine powder is preferably carbon black. The thickness of the uppermost magnetic layer is 0.5μ.
It is preferably less than m, more preferably 0.1
It is 0.4 μm.

In order to achieve the high CN ratio required for digital media, the surface roughness R _10z of the uppermost layer is 5-20.
It is preferably set to nm.

Further, since the thickness of the uppermost layer is very thin and the surface property of the uppermost layer is strongly influenced by the surface property of the lower layer, the average particle size of the nonmagnetic powder or the high magnetic permeability material used for the lower layer is , Usually 1 to 300 nm, preferably 1 to 100 nm,
More preferably, it is 1 to 50 nm. Further, it is preferable to use the Wet on wet method in which the uppermost layer is provided while at least one layer other than the uppermost layer is in a wet state. As described above, the surface of the uppermost magnetic layer can be controlled by defining the amount of the conductive fine powder in the upper and lower layers, and C
It is possible to improve the head clog characteristics at a low temperature (0 ° C.) while keeping the N ratio and the overwrite characteristics excellent, and prevent the output from decreasing under low humidity (40 ° C., 20% RH). (Layer Structure) The magnetic recording medium of the present invention basically comprises a magnetic layer which is the uppermost layer and at least one layer which exists between the magnetic layer and the non-magnetic support, on the non-magnetic support. I will do it. Incidentally, on the surface (back surface) on which the magnetic layer is not provided on the non-magnetic support, improvement in running property of the magnetic recording medium,
A back coat layer is preferably provided for the purpose of preventing electrostatic charge and transfer, and an undercoat layer may be provided between the magnetic layer and the non-magnetic support. (Non-magnetic support) Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, and cellulose derivatives such as cellulose triacetate and cellulose diacetate. Examples thereof include plastics such as polyamide and polycarbonate. The form of the non-magnetic support is not particularly limited, and is mainly a tape shape, a film shape, a sheet shape,
There are card shape, disk shape, drum shape, etc.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or a sheet, it is usually 3 to 1.
00 μm, preferably 5 to 50 μm, about 30 μm to 10 mm in the case of a disk or card, and appropriately selected depending on the recorder etc. in the case of a drum.

The non-magnetic support may have a single structure or a multi-layer structure. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment.

A backcoat layer is formed on the surface (surface) of the non-magnetic support on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. It is preferable to provide it, and as described above, an undercoat layer can be provided between the magnetic layer and the non-magnetic support. (Magnetic Layer) In the present invention, the uppermost layer is the magnetic layer. This magnetic layer is basically made of magnetic powder dispersed in a binder resin.

The uppermost magnetic layer preferably contains ferromagnetic metal powder and / or hexagonal magnetic powder. .. The film thickness of the uppermost layer is 0.8 μm or less, preferably less than 0.5 μm, more preferably 0.1 to 0.
It is 4 μm. By satisfying these conditions,
The magnetic recording medium of the present invention can improve high frequency characteristics.

The ferromagnetic metal powder used for the uppermost layer includes Fe, Co, Fe-Al system, and Fe-Al-.
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Al-Ca type, Fe-Ni type, Fe-Ni-Al
System, Fe-Ni-Co system, Fe-Ni-Si-Al-M
n-based, Fe-Ni-Si-Al-Zn-based, Fe-Al-
Si-based, Fe-Ni-Zn-based, Fe-Ni-Mn-based, F
e-Ni-Si system, Fe-Mn-Zn system, Fe-Co-
Ferromagnetic powders such as Ni-P series, Ni-Co series, and metal magnetic powders containing Fe, Ni, Co, etc. as the main components can be used. Among them, Fe-based metal powder has excellent electrical characteristics.

On the other hand, from the viewpoint of corrosion resistance and dispersibility, Fe-Al type, Fe-Al-Ca type, Fe-Al-type.
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Ni-Si-Al-Zn system, Fe-Ni-Si-A
Fe-Al-based metal powder such as 1-Mn-based is preferable.

In particular, the ferromagnetic metal powder preferred for the purpose of the present invention is a metal magnetic powder containing iron as a main component, and contains Al or Al and Ca in a weight ratio of Al to Fe:
Al = 100: 0.5 to 100: 20, and Ca is preferably contained in a weight ratio of Fe: Ca = 100: 0.1 to 100: 10.

By setting the ratio of Fe: Al in such a range, the corrosion resistance is remarkably improved, and by setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics are improved and dropout is reduced. Can be made The reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, but it is considered that the coercive force is increased and the agglomerates are decreased due to the improved dispersibility.

The ferromagnetic metal powder used in the present invention is
Its average major axis length is less than 0.25 μm, especially 0.10 to
0.22 μm, more preferably 0.10 to 0.17 μm
And the crystal size is less than 200Å, especially 100-180
It is preferably Å. The axial ratio (average major axis length / average minor axis length) is 12 or less, preferably 10 or less, and more preferably 5 to 9. When the average major axis length, crystal size, and axial ratio of the ferromagnetic metal powder are within the above ranges, the electromagnetic conversion characteristics can be further improved.

The ferromagnetic metal powder used in the present invention usually has a coercive force (Hc) of 600 to 5,000.
It is preferably in the range of Oe. This coercive force is 600
If it is less than Oe, the electromagnetic conversion characteristics may deteriorate, and if the coercive force exceeds 5,000 Oe, recording may not be possible with an ordinary head, which is not preferable.

The ferromagnetic powder preferably has a saturation magnetization (σs), which is a magnetic characteristic, usually 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, electromagnetic conversion characteristics may deteriorate.

Further, in the present invention, a ferromagnetic metal powder having a specific surface area by the BET method of 30 m ² / g or more, particularly 45 m ² / g or more is preferably used according to the higher recording density.

This specific surface area and its measuring method are described in "Measurement of powder" (JM Dallas).
e, Clyeorr Jr. Co-authored by Muta and other translations: published by Sangyo Tosho Publishing Co., Ltd.), and also described in "Chemical Handbook" Application, P1170-1171 (Chemical Society of Japan, published by Maruzen Co., Ltd., April 30, 1966). Has been done.

The specific surface area can be measured, for example, by using powder 105
Degassed while being heated at around 13 ° C for 13 minutes to remove those adsorbed on the powder, and then introduce this powder into the measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² .
Measurement is carried out with nitrogen at liquid nitrogen temperature (-105 ° C) for 10 minutes. As the measuring device, for example, a counter soap (manufactured by Yuasa Ionics Co., Ltd.) is used.

Examples of the hexagonal magnetic powder include hexagonal ferrite. Such hexagonal ferrite is composed of barium ferrite, strontium ferrite, etc., and a part of iron element is another element (for example, Ti, Co, Zn, In, Mn, Ge, H).
b)) may be substituted. Regarding this ferrite magnetic material, the IEEE Trans, on MAG-1
816 (1982).

In the present invention, particularly preferable hexagonal magnetic powder is barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder.

Preferred B which can be used in the present invention
The a-ferrite magnetic powder is Ba-ferrite powder of Fe.
Average particle size (height of diagonal of plate surface of hexagonal ferrite) in which a part of at least is replaced by Co and Zn 400
~ 900Å, plate ratio (value obtained by dividing the length of the diagonal of the plate surface of hexagonal ferrite by the plate thickness) 2.0 to 10.0, more preferably 2.0 to 6.0, coercive force (Hc ) 450-15
It is a Ba-ferrite of 00 Oe (oersted).

In the Ba-ferrite powder, the coercive force is controlled to an appropriate value by partially substituting Fe with Co, and further by partially substituting with Zn, it is not possible to obtain only by Co substitution. It is possible to obtain a magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. Further, in the Ba-ferrite used in the present invention, it does not matter if a part of Fe is further substituted with a transition metal such as Ti, In, Mn, Cu, Ge or Sn.

The Ba-ferrite used in the present invention is represented by the following general formula. BaO n ((Fe _{1 -m} M _m ) ₂ O ₃ ) [where m> 0.36 (where Co + Zn = 0.0
8 to 0.3, Co / Zn = 0.5 to 10), n is 5.4 to 11.0, preferably 5.4 to 6.0, and M represents a substituted metal, Magnetic particles that are a combination of two or more elements having an average number of 3 are preferable. In the present invention, the reason why the average particle diameter of Ba-ferrite, the plate ratio, and the coercive force are preferably within the above-mentioned preferred ranges is as follows. That is, if the average particle size is less than 400Å, the reproduction output when used as a magnetic recording medium becomes insufficient, and conversely, if it exceeds 900Å, the surface smoothness when used as a magnetic recording medium deteriorates significantly, and the noise level becomes low. If the plate ratio is less than 2.0, the perpendicular orientation ratio suitable for high density recording cannot be obtained when the magnetic recording medium is used, and conversely the plate ratio becomes 10.0. If it exceeds, the surface smoothness when used as a magnetic recording medium is significantly deteriorated, the noise level becomes too high, and the coercive force is 350.
If it is less than Oe, it becomes difficult to hold the recording signal, and 2
This is because if it exceeds 000 Oe, the head may cause a saturation phenomenon to make recording difficult.

The hexagonal magnetic powder used in the present invention usually has a saturation magnetization (σs), which is a magnetic characteristic, of 50e.
It is preferably at least mu / g. If the saturation magnetization is less than 50 emu / g, the electromagnetic conversion characteristics may deteriorate. A preferable specific example of the Ba-ferrite used in the present invention is Co-substituted Ba ferrite.

As the method for producing the hexagonal magnetic powder used in the present invention, for example, the oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite, such as boric acid, can be used. A glass-forming substance, and the resulting melt is rapidly cooled to form a glass. Then, the glass is heat-treated at a predetermined temperature to precipitate a desired Ba-ferrite crystal powder, and finally a glass component is added. In addition to the glass crystallization method of removing by heat treatment,
A coprecipitation-firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method and the like can be applied.

In the present invention, the ferromagnetic metal powder and the hexagonal magnetic powder may be mixed and used. The content of the ferromagnetic metal powder and / or the hexagonal magnetic powder in this magnetic layer is usually 50 to 99% by weight, preferably 60 to 95% by weight.

By the way, in the layers containing non-magnetic powder other than the uppermost magnetic layer, the thickness of the magnetic layer is 0.8 μm or less. Therefore, the lubricant is replenished to the uppermost magnetic layer. Function as a layer. In order for the layer below the magnetic layer to function well as a lubricant replenishing layer, the non-magnetic powder contained in the layer below the magnetic layer preferably has as little oil absorption as possible, usually 200 ml / 10.
It is 0 g or less, preferably 100 ml / 100 g or less.

In the present invention, the surface roughness R of the magnetic layer is
_10z is preferably 5 to 20 nm, but 10 to 18
nm is preferable, and 12 to 15 nm is more preferable.

Surface roughness R according to the present invention_10z And the figure
As shown in 2, the magnetic recording medium is ± 2 from the middle point P in the width direction.
Only the reference length in the longitudinal direction in the range of mm (indicated by R in the figure)
When cut vertically, the outer surface contour curve at the cut surface
No. 10 from the highest straight line parallel to the horizontal line that cuts the line
Passing the summit that is low in the eyes and the tenth shallowest valley from the deepest
Select the one that passes through the bottom, and select these two straight lines (l ₁ And l
₂ ) Is measured in the direction of the vertical magnification of the surface contour curve
It refers to the value.

To measure the above R _10z , a Taristep roughness meter (Rank Taylor Hobson Co.) is used.
As the measurement conditions, a stylus is 2.5 × 0.1 μm,
Stylus pressure 2mg, cut-off filter 0.33H
z, measurement speed 2.5 μm / sec, reference length 0.
It was set to 5 mm. The roughness curve is 0.002μ
The unevenness of m or less is cut.

R above_10z Control to 20 nm or less
To roll, for example
Control conditions to control the surface smoothness of the magnetic layer.
You can do it. That is, in this surface smoothing treatment,
Factors controlled as calender conditions are temperature, linear pressure, C
/ S (coating speed)
It As other factors, a kneading method of magnetic powder,
Surface treatment, magnetic layer The size and amount of added particles in the
It

To achieve the object of the present invention, the above temperature is usually 50 to 140 ° C. and the linear pressure is 50 to 400 Kg.
/ Cm, and the above C / S is preferably maintained at 20 to 600 m / min. If the values are out of the range, it may be difficult or impossible to specify the surface roughness of the magnetic layer as described above.

[Layer containing non-magnetic powder or layer containing high magnetic permeability material other than uppermost layer] In the present invention, a plurality of layers are formed on the non-magnetic support, and at least one layer other than the uppermost layer is formed. Preferably, the layer adjacent to the uppermost layer contains a non-magnetic powder or a high magnetic permeability material. (Non-magnetic powder) As the non-magnetic powder in the present invention,
It can be appropriately selected and used from various known non-magnetic powders used for this kind of magnetic recording medium. Examples of the non-magnetic powder include titanium oxide, barium sulfate, ZnS, MgCo ₃ , CaCO ₃ , ZnO and Ca.
O, tungsten disulfide, molybdenum disulfide, boric acid nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-A
l ₂ O ₃ , SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly , Diatomaceous earth, dolomite, and polymer powders such as polyethylene.

Of these, CaCO is preferable.
₃ , titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-
Inorganic powder such as iron oxide and polymer powder such as polyethylene. The average particle size of the non-magnetic powder is usually 1 to 3.
The thickness is 00 nm, preferably 1 to 100 nm, and particularly preferably 1 to 50 nm. It is preferable to use a non-magnetic powder having a spherical shape and an average particle diameter in the above range, since the non-magnetic powder in the non-magnetic layer does not adversely affect the surface roughness of the magnetic layer. The content of the nonmagnetic powder in the nonmagnetic layer is 5 to 99% by weight, preferably 60 to 95% by weight, particularly preferably 75 to 95% by weight, based on the total of all components constituting the nonmagnetic layer. Is. When the content of the non-magnetic powder is within the above range, the surface roughness R _10z of the uppermost layer can be good. (High permeability material) As a high permeability material, its coercive force H
It is possible to use one in which c is 0 <Hc ≦ 1.0 × 10 ⁴ [A / m], preferably 0 <Hc ≦ 5.0 × 10 ³ [A / m]. When the coercive force is within the above range, the effect of stabilizing the magnetization region of the uppermost layer is exhibited as the high magnetic permeability material. When the coercive force exceeds the above range, desired properties may not be obtained due to manifestation of properties as a magnetic material, which is not preferable.

In the present invention, it is preferable to appropriately select a material having a coercive force range as the high magnetic permeability material. Examples of such a high magnetic permeability material include a metal soft magnetic material and an oxide soft magnetic material.

Fe-S is used as the metal soft magnetic material.
i alloy, Fe-Al alloy (Alperm, Alfemo
l, Alfer), permalloy (Ni-Fe binary alloy, and multi-component alloy in which Mo, Cu, Cr, etc. are added thereto), sendust (Fe-Si-Al [9.6 wt% Si, 5. 4% Al, the balance being Fe]], Fe—Co alloy, and the like. Among them, sendust is preferable as the preferable metal soft magnetic material. The metal soft magnetic material as the high magnetic permeability material is not limited to those exemplified above, and other metal soft magnetic materials can be used. The high permeability material can be used alone, or
Also, two or more of them can be used in combination.

As the oxide soft magnetic material, spinel type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ and C are used.
oFe ₂ O _{4 ,} NiFe ₂ O _{4 ,} MgFe ₂ O _{4 ,} Li
_0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni-
Zn-based ferrite, Ni-Cu-based ferrite, Cu-Z
n type ferrite, Mg-Zn type ferrite, Li-Zn
Examples include series ferrites. Among these, Mn-Zn ferrite and Ni-Zn ferrite are preferable. These soft oxide magnetic materials can be used alone or in combination of two or more.

This high-permeability material is made into a fine powder using a ball mill or other crushing device, and its particle size is 1 nm to 3 nm.
It is preferably 00 nm, especially 1 nm to 100 nm. Particularly preferably, it is 1 to 50 nm. In order to obtain such a fine powder, the metal soft magnetic material can be obtained by spraying a molten alloy in a vacuum atmosphere. Further, the soft oxide magnetic material can be made into a fine powder by a glass crystallization method, a coprecipitation firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like.

In the layer containing the high magnetic permeability material, the content of the high magnetic permeability material is 5 to 99% by weight, preferably 50 to 95% by weight, more preferably 60 to 90% by weight. When the content of the high permeable material is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained.
If the high magnetic permeability material is less than 5% by weight, the effect as the high magnetic permeability layer may not be obtained, which is not preferable. The layer containing the high magnetic permeability material may contain non-magnetic particles.

The magnetic recording medium of the present invention contains a conductive powder. As the conductive powder, carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate,
Organic silver compounds, metal particles such as copper powder, pigments such as metal oxides such as zinc oxide, barium nitrate and titanium oxide coated with a conductive material such as tin oxide film or antimony solid solution oxide film Etc.

In the present invention, a carbon black for shading is used as carbon black, for example, Raven 2000 (specific surface area 190 m ² / g, particle size 18 mμ) manufactured by Columbia Carbon Co., Ltd. 2100, 1170, 1000, # 100 manufactured by Mitsubishi Kasei Co., Ltd. , # 75, # 40, # 35, # 30
Etc. can be used. Conductive carbon black can also be used, for example, Conductivity 975 of Columbia Carbon Co.
(BET value (hereinafter abbreviated as BET) 250 m ² / g, DB
P oil absorption (hereinafter abbreviated as DBP) 170 ml / 100 gr,
Particle size 24mμ, Conductex 900 (BET12
5 m ² / g, particle size 27 mμ), Conductex 40
-220 (particle size 20 mμ), Conductex SC (B
ET220m ² / gr, DBP115ml / 100g
r, particle size 20 mμ), Cabot vulcan (Ca
bot Vulcan) XC-72 (specific surface area 254 m
² / g, particle size 30mμ, Vulcan P (BET143m
² / gr, DBP 118 ml / 100 gr, particle size 20
mμ), Raven 1040, 420, Black Pearls 2000 (particle size 15 mμ), and Mitsubishi Kasei Co. # 44.

Another carbon black that can be used in the present invention is Conductduct-SC. Manufactured by Colombian Carbon Co. (BET22
0 m ² / g, DBP 115 ml / 100 g, particle size 20
mμ), Vulcan 9 manufactured by Cabot
(BET 140 m ² / g, DBP 114 ml / 100
g, particle size 19 mμ), Asahi Carbon Co. # 80 (BET
117 m ² / g, DBP 113 ml / 100 g, particle size 23 mμ, HS100 (BET 32 m, manufactured by Denki Kagaku)
² / g, DBP 180ml / 100g, particle size 53m
μ), # 22B manufactured by Mitsubishi Kasei (BET55m ² /
g, DBP 131 ml / 100 g, particle size 40 mμ), #
20B (BET 56m ² / g, DBP 115ml / 1
00g, particle size 40mμ, # 3500 (BET47m ²
/ G, DBP187ml / 100g, particle size 40mμ)
In addition, CF-9, # 40 manufactured by Mitsubishi Kasei Co., Ltd.
00, MA-600, Black Pearls L manufactured by Cabot, Monarch (Mo
800), Black Pearls 700, Black Pearls 1000, Black Pearls 880,
Black Pearls 900, Black Pearls 130
0, Black Pearls 2000, Sterling (St
erling) V, Raven 410, Raven 3200, Raven 430, Raven 450, Raven 825, Raven 1255, Raven 1035, Raven 1000, Raven 5000, Raven MT-P, Ketjenblack FC manufactured by Columbian Carbon Co. Etc. (Binder) Typical examples of the binder used to form the uppermost magnetic layer and layers other than the magnetic layer include vinyl chloride resins such as polyurethane and polyester vinyl chloride copolymer. It is preferable that these resins contain a repeating unit having at least one polar group selected from —SO ₃ M, —OSO ₃ M, —COOM and —PO (OM ¹ ) ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K or Li,
M ¹ represents a hydrogen atom, an alkali metal such as Na, K and Li, or an alkyl group.

The above polar group has the function of improving the dispersibility of the ferromagnetic powder, and the content in each resin is 0.1 to 8.0 mol%, preferably 0.5 to 6.0 mol%. .. When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is deteriorated, and when the content is more than 8.0 mol%, the magnetic coating tends to gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The content of the binder in the magnetic layer is usually 10 to 100 parts by weight of the ferromagnetic powder.
40 parts by weight, preferably 15 to 30 parts by weight. The binder (binder) is not limited to one kind alone, and two or more kinds can be used in combination. In this case, the ratio of polyurethane and / or polyester to vinyl chloride resin is usually 90:10 by weight. 10:90,
It is preferably in the range of 70:30 to 30:70.

The polar group-containing vinyl chloride copolymer used as a binder in the present invention is a compound having a hydroxyl group and the following polar group and chlorine atom, such as a vinyl chloride-vinyl alcohol copolymer. It can be synthesized by addition reaction with.

Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH
_{2 CH 2 OSO 3 M, Cl} -CH 2 COOM, Cl-C
_{H 2 -P (= 0) (} OM 1) taken ₂ These compounds _{Cl-CH 2 CH 2 SO 3} Na Examples, describing the reaction is as follows. _{-CH 2 C (OH) H- +} ClCH 2 CH 2 SO 3 Na
_{→ -CH 2 C (OCH 2 CH} 2 SO 3 Na) H-.

For the polar group-containing vinyl chloride copolymer, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is charged into a reaction vessel such as an autoclave to start a general polymerization. Agents, eg BPO
(Benzoyl peroxide), AIBN (azobisisobutyronitrile) and other radical polymerization initiators, redox polymerization initiators, cationic polymerization initiators and the like can be obtained by carrying out a polymerization reaction.

Specific examples of the reactive monomer for introducing the sulfonic acid or its salt include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid, and the like. Mention may be made of salt.

When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used,
When phosphoric acid or a salt thereof is introduced, for example, (meth) acrylic acid-2-phosphate ester may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so.

When an epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is 1
-30 mol% is preferable, and 1-20 mol% is more preferable. For example, chrysidyl acrylate is preferable as the monomer for introducing the epoxy group.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-57-42427 are cited.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
No. 8306, No. 60-238371, No. 62-121
No. 923, No. 62-146432, No. 62-1464.
No. 33 and the like are described, and these can be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting a polyol with a polybasic acid. By using this known method, a polyester (polyol) having a polar group can be synthesized from a polybasic acid partially having a polar group.

Examples of polybasic acids having polar groups include 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Examples thereof include sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and their sodium salts and potassium salts.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, 1.3-butanediol, 1.4-butanediol, 1 6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like can be mentioned.

Incidentally, other polar group-introduced polyesters can also be synthesized by a known method.

Next, polyurethane will be described. It results from the reaction of polyols with polyisocyanates. As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, if a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1.5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like can be mentioned.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective. _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OS
_{O 2 M, Cl-CH 2} COOM, Cl-CH 2 -P (=
0) (OM ¹ ) _{2 As} a technique for introducing a polar group into polyurethane, JP-B-58-41565 and JP-A-57-9242 are known.
No. 2, No. 57-92423, No. 59-8127, No. 59-5423, No. 59-5424, No. 62-12.
It is described in the publications such as 1923, and these can be used in the present invention.

In the present invention, the following resins can be used together as a binder in an amount of 20% by weight or less based on the total amount of the binder.

The resin has a weight average molecular weight of 1
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (nitrocellulose etc.), styrene-butadiene copolymers, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins, various synthetic rubber resins, etc. .. (Other Components) In the present invention, in order to improve the durability of the magnetic layer, polyisocyanate is preferably contained in the magnetic layer.

Examples of the polyisocyanate include aromatic polyisocyanates such as adducts of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI) and active hydrogen compounds, hexamethylene diisocyanate (HMDI) and active hydrogen compounds. There are aliphatic polyisocyanates such as adducts of. The weight average molecular weight of the polyisocyanate is 100 to 3,000.
It is desirable to be in the range of 0.

In the present invention, the magnetic layer may optionally contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent and a filler.

First, as the dispersant, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, and other aliphatic groups having 12 to 18 carbon atoms; salts of these alkali metals or alkaline earth Metal salts or their amides: polyalkylene oxide alkyl ester; lecithin; trialkyl polyolefinoxy quaternary ammonium salt: azo compounds having a carboxyl group and a sulfonic acid group. These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

Next, a fatty acid and / or a fatty acid ester can be used as the lubricant. In this case, the amount of the fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder. If the addition amount is less than 0.2% by weight, the running property is likely to deteriorate,
If it exceeds 10% by weight, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to decrease.

The amount of the fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder. If the addition amount is less than 0.2% by weight, the still durability is apt to deteriorate, and if it exceeds 10% by weight, the fatty acid ester is likely to seep out to the surface of the magnetic layer or the output tends to be lowered.

When it is desired to use a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid and preferably has 6 to 30 carbon atoms.
The range of -22 is more preferable.

Specific examples of the fatty acid include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid. Acid, maleic acid, glutaric acid, adipic acid,
Examples thereof include pimelic acid, azelaic acid, sebacic acid, 1.12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like.

Specific examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate. Tate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2.
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol-mono-butyl ether palmitate, diethylene glycol mono- Butyl ether palmitate and the like.

As the lubricant other than the above fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

Specific examples of the abrasive include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The average particle size of the abrasive is preferably 0.05 to 0.6 μm, more preferably 0.1 to 0.3 μm.

As the antistatic agent, conductive powder such as carbon black and graphite; cationic surfactant such as quaternary amine; acid such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid. Anionic surfactants containing a group; amphoteric surfactants such as aminosulfonic acid; natural surfactants such as saponin.

The above-mentioned antistatic agent is usually added in the range of 0.01 to 40% by weight with respect to the binder. (Manufacture of Magnetic Recording Medium) The magnetic recording medium of the present invention is not particularly limited in its manufacturing method, and may be manufactured according to a known method used for manufacturing a single-layer or multi-layer structure type magnetic recording medium. it can.

For example, generally, a ferromagnetic powder, a binder,
A magnetic coating material is prepared by kneading and dispersing a dispersant, a lubricant, an abrasive, an antistatic agent and the like in a solvent, and then the magnetic coating material is applied to the surface of the non-magnetic support.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate. Cyclic ethers such as tetrahydrofuran; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, dihydrobenzene, and other halogenated hydrocarbons can be used. Various kneading and dispersing machines can be used for kneading and dispersing the magnetic layer forming components.

Examples of the kneading / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill,
Kobol mill, tron mill, sand mill, sand grinder, Sqegvari attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, high speed mixer, homogenizer, ultrasonic disperser, open kneader, continuous kneader, pressure kneader, etc. Can be mentioned.

Of the above kneading and dispersing machines, 0.05 to 0.5
Kneading dispersers capable of providing a power consumption load of KW (per 1 kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill.

To coat a magnetic layer on a non-magnetic support,
In producing the magnetic recording medium of the present invention, it is preferable to perform simultaneous multi-layer coating by the wet-on-wet multi-layer coating method from the viewpoint of the effect. Specifically, as shown in FIG. 3, first, each coating material of the magnetic layer is wet-on-wet type on the film-shaped support 1 fed from the supply roll 32 by the extrusion type extrusion coaters 10 and 11. After the multi-layer coating, it passes through the orientation magnet or the vertical orientation magnet 33, is introduced into the dryer 34, and hot air is blown from the nozzles arranged above and below to dry it.
Next, the dried support 1 with each coating layer is combined with a calender roll 38 to form a super calender device 37.
And is subjected to calendar processing here, and then wound up on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce, for example, a magnetic recording tape for an 8 mm video camera.

In the above-mentioned method, each coating material was extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. In the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coater 1
0 and 11 are provided with liquid reservoirs 13 and 14, respectively,
Overlay the paint from each coater in a wet-on-wet fashion. That is, the upper magnetic layer coating material is applied in multiple layers immediately after the lower magnetic layer coating material is applied (when it is in an undried state). The coater head shown in FIG. 4C is preferable in the present invention.

As the wet-on-wet multilayer coating method, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can be used. Furthermore, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, etc. can be combined.

In the multi-layer coating by the wet-on-wet method, since the upper magnetic layer is coated while the lower layer remains wet, the surface of the lower layer (that is, the boundary surface between the upper layer) and the upper layer are smoothed. The surface property of is improved, and the contact between the upper and lower layers is also improved. As a result,
Especially for high density recording, high output and low noise are required, for example, the performance required as a magnetic tape is satisfied, and high durability performance is required. Strength is improved and durability is sufficient. Further, the wet-on-wet multi-layer coating method can also reduce dropout and improve reliability.

As the solvent to be added to the above paint or a diluent solvent for applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol: methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol cenoacetate: ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran: aromatic hydrocarbons such as benzene, toluene, xylene: methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
A halogenated hydrocarbon such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more.

The magnetic field in the orienting magnet or the vertically orienting magnet is about 20 to 5,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes. Is.

Next, a surface smoothing process is performed by calendering. After that, if necessary, burnishing or blade processing is performed for slitting. At this time, the surface smoothing treatment is effective for achieving the object of the present invention.

That is, as described above, one of the essential requirements of the present invention is the condition of the roughness of the surface of the magnetic layer. To satisfy this condition, this surface smoothing treatment is preferable.
In the surface smoothing treatment, temperature, linear pressure, C / S (coating speed) and the like can be mentioned as calendering conditions.

To achieve the object of the present invention, the above temperature is usually 50 to 120 ° C., and the above linear pressure is 50 to 400 k.
It is preferable to keep g / cm and the above C / S at 20 to 600 m / min. If the value is out of the range, it may be difficult or impossible to specify the surface state of the magnetic layer as in the present invention.

[0094]

According to the present invention, it is possible to obtain a magnetic recording medium having excellent head clog characteristics at low temperatures and excellent output lowering preventive ability at low humidity.

[0095]

EXAMPLES Examples of the present invention will be described below.

The components, ratios, and operation sequences shown below can be variously modified without departing from the scope of the present invention. In the following examples, all "parts" are parts by weight.

Example 1 Each component of the magnetic composition for the upper layer below was kneaded and dispersed using a kneader sand mill to prepare a magnetic coating material for the upper layer. [Upper layer coating material A] Fe-Al based ferromagnetic metal powder 100 parts (Fe: Al weight ratio = 100: 8, average major axis length: 0.16 μm, Hc: 1580 Oe, σs: 120 emu / g, axial ratio 8 Crystallite size: 170Å) Vinyl chloride resin containing sulfonic acid metal salt 10 parts [Nippon Zeon Co., Ltd., MR-110] Polyester polyurethane resin containing sulfonic acid metal salt [Toyobo Co., Ltd., UR-8700] 5 parts Alumina (α-Al ₂ O ₃ , average particle size: 0.2 μm) 6 parts Carbon black [Average particle size and weight are listed in Table 1] Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts 100 parts toluene [layer-coating material D] SnO ₂ instead of the carbon black in the layer-coating material a (average particle size 5 nm) except for using 0.4 parts it is the same as A. [Lower layer coating C] TiO ₂ (average particle size 30 nm) 100 parts Carbon black (described in Table 1) Vinyl chloride resin containing sulfonic acid metal salt 6 parts [Nippon Zeon Co., Ltd., MR-110] Sulfonic acid metal salt Containing Polyester Polyurethane Resin [Toyobo Co., Ltd., UR-8700] 3 parts Alumina 6 parts (α-Al ₂ O ₃ , average particle size: 0.2 μm) Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 Parts Toluene 100 parts [Upper layer coating material B] Co-substituted barium ferrite (H) instead of the Fe-Al based ferromagnetic metal powder in the upper layer coating material A
c: 1100 Oe, BET 45 m ² / g, σs: 6
Same as A except that 4 emu / g, plate ratio 4) was used. [Lower Layer Coating E] Same as C except that in the lower layer coating C, 0.4 part of SnO ₂ (average particle size 25 nm) was used instead of carbon black. In [undercoating paint F] Paint C underlayer in place of TiO ₂ Fe-Si-Al sendust alloy powder (coercivity Hc
= 40 A / m, μi = 200 H / m, particle size 50 nm), and the same as C. [Lower Layer Coating Material G] In the lower layer coating material C, Co—Fe ₂ O ₃ (average particle size 0.16 μm, crystallite size 330Å, Hc: 800 Oe, σs: 78e) was used instead of TiO _2.
The same as C except that mu / g) was used.

Next, 5 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the obtained upper layer magnetic coating material and lower layer coating material, and then the thickness was 10 μm by a wet-on-wet method. After coating on the polyethylene terephthalate film of, the magnetic field orientation treatment is performed while the coating film is undried, followed by drying, followed by surface smoothing with a calendar,
A magnetic layer composed of a lower layer having a thickness of 2.0 μm and an upper layer having a thickness of 0.4 μm was formed.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene phthalate film opposite to the magnetic layer, the coating film is dried, and calendering is performed according to the calendering conditions described later. A 0.8 μm thick back coat layer was formed to obtain a wide original magnetic tape. [Backcoat layer coating material] Carbon black 40 parts (Raven 1035) Barium sulfate 10 parts (Average particle size 300 mμ) Nitrocellulose 25 parts Polyurethane resin 25 parts (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) Polyisocyanate compound 10 Parts (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The raw material thus obtained was slit to prepare an 8 mm video tape.

The electromagnetic conversion characteristics, coating properties and running durability of this video tape were measured as follows. The results are shown in Table 1. (CN characteristic) A single wave of 9 MHz was recorded, and the output level when the signal was reproduced was expressed by comparison with the reference sample (Comparative Example 1). (Overwrite characteristics) A residual output level of a 2 MHz signal when a 2 MHz signal was recorded at a saturation level and then a 9 MHz signal was (overwritten) recorded was measured. The lower the residual output level, the better the overwrite characteristic. (Head clog at low temperature) S-550 under 0 ℃ environment
(Sony), run the tape for the entire length, and
The head was clogged when the output was continuously decreased for 2 dB or more for 1 second or more, and the number of times was counted. (Reduction of RF output under low humidity (40 ° C, 20% RH)) 4
S-550 (manufactured by Sony Corporation) in an environment of 0 ° C and 20% RH
The tape was run for two full lengths and the RF output reduction (dB) before and after running was measured.

[0101]

[Table 1]

[Brief description of drawings]

FIG. 1 is an example of a cross-sectional view of a magnetic recording medium.

FIG. 2 is a diagram illustrating a situation when measuring a surface roughness R _10z of a magnetic layer.

FIG. 3 is a diagram for explaining simultaneous multi-layer coating of magnetic layers by a wet-on-wet coating method.

FIG. 4 is a view of a coater head for applying a magnetic layer paint.

[Explanation of symbols]

 1 Support 2 Magnetic Layer 3 Backcoat Layer 4 Intermediate Layer

Claims (2)

[Claims] 1. A plurality of layers are formed on a non-magnetic support, the thickness of the uppermost magnetic layer is 0.8 μm or less, and 100 parts by weight of conductive fine powder is magnetic powder. For 0.
1 to 1.0 parts by weight, and at least one layer other than the uppermost layer is a layer containing a non-magnetic powder or a high-permeability material. A magnetic recording medium containing less than 1.0 part by weight of powder. 2. The magnetic recording medium according to claim 1, wherein the thickness of the uppermost magnetic layer is less than 0.5 μm.