JP3451277B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic recording medium.
More specifically, the present invention relates to a magnetic recording medium excellent in RF output, CN ratio, and running durability under high temperature and high humidity (40 ° C., 80% RH) required as a medium for digital VTR.

[0002]

BACKGROUND OF THE INVENTION A conventional magnetic recording medium is one in which a magnetic powder is made into a fine powder, or an upper layer is a magnetic layer,
High quality has been achieved by forming a so-called multi-layer structure in which the lower layer is a non-magnetic layer (JP-A-63-1).
87418).

In the technique described in Japanese Patent Laid-Open No. 63-187418, since the Vickers hardness of the uppermost magnetic layer is not sufficiently controlled, it is possible to obtain the CN ratio and the RF output required as a medium for a digital VTR. It is not possible, and the running durability under various environments cannot be guaranteed. Further, in the present invention, the thickness of the uppermost magnetic layer is less than 0.5 μm,
The thickness is preferably 0.1 to 0.3 μm to reduce the film thickness loss and to obtain the RF output and the CN ratio required as a medium for a digital VTR. Further, by forming a layer containing a non-magnetic powder or a material having a high magnetic permeability in the lower layer, self-demagnetization can be prevented and a high CN ratio and a high RF output can be obtained.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems and to provide excellent RF output, CN ratio, and running durability under high temperature and high humidity (40 ° C., 80% RH) required as a medium for digital VTR. Another object is to provide a magnetic recording medium suitable as a digital recording medium.

[0005]

A magnetic recording medium according to the present invention for achieving the above object has the following constitution. (1) An upper layer and a lower layer are formed on a non-magnetic support, and the upper layer is
A magnetic layer formed by dispersing magnetic powder in a binder,
Vickers hardness of the magnetic layer is 40 or more and less than 200, the lower layer I nonmagnetic layer der containing nonmagnetic powder, non magnetic
The magnetic recording medium of Vickers hardness sex layer has a 30-100 der Rukoto. (2) The Vickers hardness of the upper layer is in the range of 5 or more and 105 or less than the Vickers hardness of the lower layer containing the non-magnetic powder.
2. The magnetic recording medium as described in 1 above, which is high . (3) The film thickness of the upper magnetic layer is 0.1 μm or more and 0.5.
The magnetic recording medium of the 1, wherein μm below der Ru. (4) While the lower layer containing the non-magnetic powder is in a wet state
4. The magnetic recording medium according to any one of 1 to 3, wherein an upper layer is provided on the magnetic recording medium.

[0006]

DETAILED DESCRIPTION OF THE INVENTION According to the research conducted by the present inventor, the technique of Japanese Patent Laid-Open No. 187418/1988 does not control the Vickers hardness of the upper and lower layers.
It was found that the RF output as the medium for R and the running durability were not good.

The present inventor has made earnest studies on a phenomenon in which the magnetic layer surface is highly smoothed to increase the true contact area by pressing with a head, a guide pin or the like, and as a result, the hardness of the magnetic layer is increased. The inventors have found that the increase in the true contact area can be effectively suppressed, and have completed the present invention.

According to the present invention, the Vickers hardness of the magnetic layer is set to 40 or more and less than 200 for the upper layer and 30 to 100 for the lower layer so that the magnetic layer is less likely to be deformed and an increase in the true contact area is suppressed. In addition, it is possible to reduce the space loss by improving the contact property of the medium with respect to the head.

On the other hand, if the Vickers hardness of the magnetic layer is less than 40 in the upper layer or less than 30 in the lower layer,
Even if the surface roughness of the magnetic layer is increased, the magnetic layer is easily deformed to increase friction and cause trouble. Further, when the Vickers hardness is 200 or more in the upper layer or exceeds 100 in the lower layer,
When the head comes into contact with the medium, the medium is stiff and jumps, resulting in a large space loss between the two, and so-called hitting of the head causes abnormal image quality.

In the present invention, the Vickers hardness of the magnetic layer in the upper layer is 50 to 1 in order to further enhance the above effects.
60, 40 to 80 in the lower layer, 70 to 70 in the upper layer
140, and it is more preferable that the lower layer has a thickness of 50 to 100.

In the present invention, the above Vickers hardness is defined as follows. That is, a diamond triangular pyramid needle is pushed in by the piezoelectric actuator under the following conditions using the following indenter.

Indenter shape: Opposite ridge angle 80 ° Triangle indenter load: 0.1 mg to 0.2 g Pushing speed: 1 to 25 nm / sec Measuring environment: 20 to 40 ° C./40 to 90% RH Pushing depth: Within 3 μm from the surface At this time, when the indentation depth when the indentation is performed by the load W is X, the following equation is established with the hardness at the depth ε being H (ε).

W (X) = a∫H (ε) (X-ε) dε a: W (X) = 1 / 2aHX ² if the material is a uniform material without constant hardness change. The graph of the load W (X) with respect to the power is a straight line, and H (Vickers hardness) can be obtained from the slope.

The Vickers hardness of the lower layer is measured as follows. That is, after removing the upper layer with a blade or a rotating polishing device, the Vickers hardness of the lower layer is measured in the same manner as the upper layer.

Further, in the present invention, it is preferable that the value of Vickers hardness of the upper layer is larger than the value of Vickers hardness of the lower layer by a range of 5 or more and 105 or less, preferably 10 or more, more preferably 15 or more. By setting the Vickers hardness of the lower layer slightly lower than that of the upper layer in this way, the lower layer acts like a cushioning material, so it is possible to prevent head hits even when the hardness of the magnetic layer surface is high. Becomes

In order to set the Vickers hardness of the upper layer and the lower layer in the above range, the crystallization temperature (Tg) of the resin used as a binder (described below) is set to -30 to -30.
There is a method of adjusting to 80 ° C. This crystallization temperature can be adjusted by changing the amount of isocyanate in the component in the case of polyurethane resin, for example. Also,
Adjustment of temperature conditions during calendaring is also effective.

As another method, there is a method in which a polar group described below is introduced into the binder resin to adjust the dispersibility of the magnetic powder.

(Layer Structure) The magnetic recording medium of the present invention basically comprises a magnetic layer which is an upper layer and a lower layer which exists between the magnetic layer and the non-magnetic support on a non-magnetic support. Formed. A back coat layer is preferably provided on the surface (back 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. Further, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

(Nonmagnetic Support) As the material for forming the nonmagnetic support, for example, polyesters such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Cellulose derivative, polyamide,
Examples include plastics such as polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, card-like,
There are disc shape and drum shape.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3 to 1.
00 μm, preferably 4 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.

[0023]

(Magnetic Layer) In the present invention, the upper layer is a magnetic layer. This magnetic layer is basically formed by dispersing magnetic powder in a binder (binder resin).

The upper magnetic layer preferably contains ferromagnetic iron oxide powder / ferromagnetic metal powder and / or hexagonal magnetic powder (preferably tabular). The thickness of the upper layer is preferably 0.1 μm or more and less than 0.5 μm, more preferably 0.1 to 0.4 μm.

As the ferromagnetic iron oxide powder, γ-Fe is used.
₂ O ₃ , Fe ₃ O ₄ , or FeO with an intermediate iron oxide
_x (1.33 < _x <1.5) or those to which Co is added (cobalt-modified) Co-FeO
Examples include those represented by _x (1.33 < _x <1.5).

The ferromagnetic metal powder used for the upper layer includes Fe, Co, Fe-Al system, Fe-Al-
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Al-Ca system, Fe-Ni system, 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-based, Ni-Co-based, metal magnetic powders containing Fe, Ni, Co, etc. as main components are exemplified. 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-Co system, Fe-Ni-Co-A
Fe-Al based metal powder such as 1-Ca based is preferable.

Particularly preferred ferromagnetic metal powders for the purpose of the present invention are metal magnetic powders containing iron as a main component, and Al or Al and Ca, and Al in a weight ratio of 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 has an average major axis length of less than 0.30 μm, particularly 0.10 to 0.
20 μm, more preferably 0.10 to 0.17 μm and crystallite size less than 200Å, especially 100 to 180Å
Is preferred. 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, crystallite 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 O.
It is preferably in the range of e. This coercive force is 600
When it is less than Oe, the electromagnetic conversion characteristics may be deteriorated, and when 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 amount is less than 70 emu / g, the electromagnetic conversion characteristics may deteriorate. In the case of a ferromagnetic metal powder, it is preferably 120 emu / g or more.

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 Co., Ltd.), and also described in "Chemical Handbook," Applied Edition, 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 a powder of 105
The mixture was deaerated while heat-treated at about 13 ° C for 13 minutes to remove what was adsorbed on the powder, and then this powder was introduced into a measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² . Measurement is performed 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. Further, as a preferable structure of the ferromagnetic powder, the content ratio of Fe atoms and Al atoms contained in the ferromagnetic powder is F in atomic ratio.
e: Al = 100: 1 to 100: 20, and the content ratio of Fe atoms and Al atoms present in the surface region of 100 Å or less at the analysis depth by ESCA of the ferromagnetic powder is Fe: It has a structure of Al = 30: 70 to 70:30. Or Fe atom, Ni atom and A
1 atom and Si atom are contained in the ferromagnetic powder, and further C
At least one of o atom and Ca atom is contained in the ferromagnetic powder, the content of Fe atom is 90 atom% or more, the content of Ni atom is 1 atom% or more, less than 10 atom%, the content of Al atom. Is 0.1 atomic% or more and less than 5 atomic%, the content of Si atoms is 0.1 atomic% or more and less than 5 atomic%, the content of Co atoms and / or the content of Ca atoms (however, Co
(This total amount when both atoms and Ca atoms are included)
Is 0.1 atomic% or more and less than 13 atomic%, and Fe atoms, Ni atoms, Al atoms, Si atoms, Co atoms and / or Fe atoms, Ni atoms, Al atoms, Si atoms and / or Co atoms present in a surface region of 100 Å or less in ESCA analysis depth of the ferromagnetic powder The content ratio of Ca atoms is Fe: Ni: Al: Si (Co and / or C in terms of atomic number ratio).
a) = 100: (4 or less): (10-60): (10
70): a ferromagnetic powder having a structure of (20 to 80).

Examples of the hexagonal magnetic powder preferably used in the present invention include hexagonal ferrite. Such hexagonal ferrite is composed of barium ferrite, strontium ferrite, etc., and a part of iron element is other element (for example, Ti, Co,
Zn, In, Mn, Ge, Hb, etc.). For this ferrite magnetic material, refer to IEEE T
trans, on MAG-18 16 (1982).

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

Preferred Ba that can be used in the present invention
-Ferrite magnetic powder is an average particle size (diagonal length of plate surface of hexagonal ferrite) of Ba-ferrite powder in which a part of Fe is replaced by at least Co and Zn.
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) 450-150
0 is Ba-ferrite.

In the Ba-ferrite powder, the coercive force is controlled to an appropriate value by partially replacing Fe with Co, and further by partially replacing it with Zn, it is not possible to obtain it only by Co substitution. A magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics can be obtained. 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, a part of Fe is T
It may be substituted with a transition metal such as i, In, Mn, Cu, Ge and 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, and m is a value smaller than 1. ), N is 5.4 to 11.0, preferably 5.4 to 6.0, M represents a substituted metal, and is a combination of two or more elements whose average number is 3. Magnetic particles are preferred. In the present invention, the reason why it is preferable that the average particle diameter of Ba-ferrite, the plate ratio, and the coercive force be within the above-mentioned preferable ranges is as follows. That is, if the average particle size is less than 300Å, 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 of the magnetic recording medium is significantly deteriorated and the noise level becomes too high.
Further, when the coercive force is less than 450 Oe, it becomes difficult to retain the recording signal, and when it exceeds 1500 Oe, the head may cause a saturation phenomenon to make recording difficult.

The hexagonal magnetic powder used in the present invention is
The saturation magnetization (σs), which is a magnetic property, is usually 50 emu.
/ G or more is desirable. This saturation magnetization is 50
If it is less than emu / g, the electromagnetic conversion characteristics may deteriorate.

A preferred specific example of the Ba-ferrite used in the present invention is Co-substituted Ba ferrite.

As a 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 are used, such as boric acid. The glass melt is melted together with another glass-forming substance, the resulting melt is rapidly cooled to form glass, and the glass is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the 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 iron oxide powder / ferromagnetic metal powder and the hexagonal magnetic powder may be mixed and used.

The content of ferromagnetic iron oxide powder / ferromagnetic metal powder and / or hexagonal magnetic powder in this magnetic layer is usually 50 to 99% by weight, preferably 60 to 99% by weight. And particularly preferably 75 to 90% by weight.

[Lower Layer Containing Non-Magnetic Powder] In the present invention, the upper layer and the lower layer are formed on the non-magnetic support, and the lower layer other than the upper layer, preferably the lower layer adjacent to the upper layer, comprises the non-magnetic powder. Is included.

(Non-Magnetic Powder) As the non-magnetic powder in the present invention, from the various known non-magnetic powders used in this kind of magnetic recording medium, those having the above-mentioned characteristics are appropriately selected and used. You can As this non-magnetic powder,
For example, carbon black, graphite, titanium oxide, barium sulfate, ZnS, MgCo ₃ , CaCO ₃ ,
ZnO, CaO, tungsten disulfide, molybdenum disulfide, boric acid nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂
O ₃ , α-Al ₂ O ₃ , SiC, cerium oxide, corundum, artificial diamond, α-iron oxide (α-Fe ₂ O
₃ ), α-FeOOH, garnet, silica, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly, diatomaceous earth, dolomite, and polymer powders such as polyethylene. Can be mentioned.

Of these, preferred are carbon black, CaCO ₃ , titanium oxide, barium sulfate and α-.
Al ₂ O ₃ , α-iron oxide (α-Fe ₂ O ₃ ), α-Fe
Inorganic powders such as OOH and Cr ₂ O ₃ and polymer powders such as polyethylene.

In the present invention, it is more preferable to use a non-magnetic powder having a needle-like powder shape in the lower layer. When the acicular non-magnetic powder is used, the surface smoothness of the non-magnetic layer (lower layer) can be improved, and the surface smoothness of the upper layer composed of the magnetic layer laminated thereon can also be improved. It is preferable because it is possible.

The major axis diameter of the nonmagnetic powder is usually 0.50 μm or less, preferably 0.40 μm or less, and particularly preferably 0.30 μm or less.

The minor axis diameter of the non-magnetic powder is usually 0.10 μm or less, preferably 0.08 μm or less, and particularly preferably 0.06 μm or less.

The axial ratio of the non-magnetic powder is usually 2 to
It is 20, preferably 5 to 15, and particularly preferably 5 to 10. The axial ratio referred to here is the ratio of the major axis diameter to the minor axis diameter (major axis diameter / minor axis diameter).

The specific surface area of the non-magnetic powder is usually 10 to 250 m ² / g, preferably 20 to 150.
m ² / g, particularly preferably 30 to 100 m ² / g
Is.

When the non-magnetic powder having the major axis diameter, the minor axis diameter, the axial ratio and the specific surface area within the above ranges is used, the surface property of the lower layer, which is the non-magnetic layer, can be improved, and the It is preferable that the surface properties of the upper layer can be in a good state.

Further, in the present invention, the non-magnetic powder is preferably surface-treated with a Si compound and / Al compound. When the non-magnetic powder subjected to such surface treatment is used, the surface condition of the upper layer composed of the magnetic layer can be improved. Said Si and / or Al
The content of Si is preferably 0.1 to 50% by weight of Si and 0.1 to 50% by weight of Al with respect to the non-magnetic powder.

The average particle size of the non-magnetic powder is usually 1 to 300 nm, preferably 1 to 100 nm, and particularly preferably 1 to 50 nm. It is preferable to use a non-magnetic powder having an average particle diameter within the above range, since the non-magnetic powder in the non-magnetic layer (lower layer) does not adversely affect the surface properties of the magnetic layer (upper layer).

The content of the non-magnetic powder in the non-magnetic layer (lower layer) is 5 to 99% by weight, preferably 60 to 99% by weight based on the total amount of all components constituting the non-magnetic layer (lower layer).
95% by weight, particularly preferably 75 to 95% by weight.
When the content of the non-magnetic powder is within the above range, the surface condition of the upper layer composed of the magnetic layer can be improved.

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

The magnetic recording medium of the present invention preferably contains a conductive powder. As the conductive powder, carbon black, graphite, tin oxide, silver powder,
Silver oxide, silver nitrate, organic compounds of silver, metal particles such as copper powder, etc., pigments such as zinc oxide, barium nitrate, titanium oxide and other metal oxides, tin oxide film, or conductive material such as antimony solid solution oxide film There are some that have been coated with.

The average particle size of the conductive fine powder is
5 to 700 nm, more preferably 5 to 200 nm
Is.

The content of the conductive fine powder is 1 to 20 parts by weight with respect to 100 parts by weight of the non-magnetic powder,
It is more preferably 5 to 15 parts by weight.

(Binder) As the binder (binder) used to form the upper magnetic layer and / or the lower layer, for example, vinyl chloride resin such as polyurethane, polyester, vinyl chloride copolymer and the like. etc. are those typical, these resins are _{-SO 3 M, -OSO 3 M,} -COOM and -OP
In order to achieve the object of the present invention, it is preferable to include a repeating unit having at least one polar group selected from O (OM ¹ ) ₂ and —PO (OM ¹ ) ₂ . Particularly, it is preferable to adjust the crystallization temperature (Tg) of the binder resin to -30 to 80 ° C.

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 or an alkali atom such as Na, K or Li.

The 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 0.2 to 6.0 mol%. . When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is lowered, 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 5 to 4 with respect to 100 parts by weight of the ferromagnetic powder.
It is 0 part by weight, preferably 10 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 the polyurethane and / or polyester to the vinyl chloride resin is usually 90: It is 10 to 10:90, and preferably 70:30 to 30:70.

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

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 ) _{2 From} these compounds, Cl-CH ₂ CH ₂ SO ₃ Na is taken as an example, and the above reaction is described as follows.

-CH ₂ C (OH) H- + ClCH ₂ CH
_{S 2 O 3 Na → -CH 2} C (OCH 2 CH 2 SO 3 N
a) H- Incidentally, M and M ¹ described above are M described in paragraph [0071].
And M ¹ having the same meaning, M is a hydrogen atom or Na,
K and Li represent an alkali metal, and M ¹ represents a hydrogen atom and Na, K, Li and other alkali atoms.

The polar group-containing vinyl chloride copolymer is prepared by charging a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced 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. As the monomer for introducing an epoxy group, for example, chrysidyl acrylate is preferable.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, see JP-A-57-44227 and JP-A-57-42427.
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 the polyester and polyurethane used as required in the present invention will be described. In general,
Polyesters are obtained by reacting polyols with polybasic acids. A polyester (polyol) having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group using a known method.

Examples of the polybasic acid having a polar group include 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Mention may be made of sulfoisophthalic acid, 3-sulfophthalic acid and their sodium 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, the polyurethane will be described.

It is obtained 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, when 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, and the amount of these isocyanates should be changed. Thus, the Vickers hardness range of the present invention can be achieved.

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 3 M, Cl-CH 2} COOM, Cl-CH 2 -P (=
0) (OM ¹ ) _{2 where} M and M ¹ are M described in paragraph [0071].
And M ¹ having the same meaning, M is a hydrogen atom or Na,
K and Li represent an alkali metal, and M ¹ represents a hydrogen atom and Na, K, Li and other alkali atoms. As a technique for introducing a polar group into polyurethane, Japanese Patent Publication No. 58-41565, JP-A Nos. 57-92422, 57-92423, 59-8127 and 59-5.
No. 423, No. 59-5424, No. 62-121923.
The publications such as the No. etc. can be used in the present invention.

In the present invention, the following resins can be used in combination as the binder (preferably 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 achieve the object of the present invention such as improving the durability of the magnetic layer,
It is desirable to include polyisocyanate in the magnetic layer.

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

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 polyolefin oxyquaternary 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, fatty acids and / or fatty acid esters 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 tends to deteriorate,
On the other hand, if it exceeds 10% by weight, the fatty acid is likely to seep out to the surface of the magnetic layer and the output is likely to decrease.

The amount of 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 likely 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 is likely to decrease.

When a fatty acid and a fatty acid ester are used in combination 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,
6-30 are preferable and, as for carbon number, the range of 12-22 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 and succinic acid. Acid, maleic acid, glutaric acid, adipic acid,
Examples thereof include pimelic acid, azelaic acid, sebacic acid, 1.12-dodecanedicarboxylic acid and octanedicarboxylic acid.

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-mentioned fatty acid and fatty acid ester, 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 polishing agent 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 diameter of the abrasive is preferably 0.05 to 0.6 μm, more preferably 0.1 to 0.3 μm.

The content of the abrasive in the lower layer is usually 3 to 20 parts by weight, preferably 5 to 15 parts by weight, and particularly preferably 5 to 10 parts by weight.

Next, 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. Examples thereof include anionic surfactants containing a group; amphoteric surfactants such as aminosulfonic acid; and 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.

(Production of Magnetic Recording Medium) The production method of the magnetic recording medium of the present invention is not particularly limited, and it is produced according to a known method used for producing a single-layer or multi-layer structure type magnetic recording medium. In particular, the wet-on-wet coating method is preferable for achieving the object of the present invention.

For example, generally, ferromagnetic powder, 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, halogenated carbon hydrogen such as dichlorobenzene, and the like can be used.

In kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used.

Examples of this kneading / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill,
Cobol 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 dispersers, 0.05 to 0.5
The 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 the production of the magnetic recording medium of the present invention, simultaneous multi-layer coating by the wet-on-wet multi-layer coating method is preferable from the viewpoint of the effect. Specifically, as shown in FIG. 1, first, each coating material of the magnetic layer is wet-on-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 by the wet method, it passes through the orienting magnet or the vertically orienting magnet 33 and is introduced into the dryer 34, where hot air is blown from the nozzles arranged above and below to dry it. Next, the dried support 1 with each coating layer is guided to a super calender device 37 including a combination of calender rolls 38, where it is calendered and then wound 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 method, each coating material was extruded through an in-line mixer (not shown) and the coater 10,
11 may be supplied. In the figure, 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 layer magnetic layer coating material is applied in multiple layers immediately after the lower layer coating material is applied (when it is in an undried state).

The coater head shown in FIG. 2 (c) 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. Further, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater and the like 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 is in a wet state, 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, 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 10000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes. .

Next, a surface smoothing process is performed by calendering.

Thereafter, if necessary, burnishing or blade processing is performed and slitting is performed.
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 surface roughness of the magnetic layer. To satisfy this condition, this surface smoothing treatment is preferable. In the surface smoothing treatment, temperature as a calender condition,
Examples include linear pressure and C / S (coating speed).

To achieve the object of the present invention, the temperature is usually 50 to 140 ° C., preferably 80 to 130 ° C., and the linear pressure is 50 to 400 kg / cm, preferably 100.
~ 400 kg / cm, C / S above 20-1000 m /
It is preferable to keep the minute. 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.

In the present invention, the Vickers hardness range of the present invention can be achieved by adopting the above preferable calender temperature conditions.

[0125]

According to the present invention, the RF output, CN ratio, and high temperature and high humidity (40
It is possible to provide a magnetic recording medium having excellent running durability under conditions of 80 ° C. and 80% RH.

[0126]

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 The following components were kneaded and dispersed using a kneader sand mill to prepare an upper layer magnetic coating material and a lower layer coating material.

[Magnetic coating for the uppermost layer] Fe-Al based ferromagnetic metal powder 100 parts (Fe: Al atomic number ratio = 100: 4 (whole), Fe: Al atomic number ratio = 50: 50 (surface layer) average length Shaft diameter: 0.14 μm, Hc: 1780 Oe, BET: 55 m ² / g) Potassium sulfonate group-containing vinyl chloride resin 10 parts [Nippon Zeon Co., Ltd., MR-110] Sodium sulfonate group-containing polyurethane resin 10 Part [Toyobo Co., Ltd., UR-8700] α-alumina (0.2 μm) 8 parts Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

[Nonmagnetic Coating for Lower Layer] 100 parts of α-Fe ₂ O ₃ (major axis diameter: 0.27 μm, minor axis diameter: 0.03 μm, axial ratio: 9, BET: 39 m ² / g) potassium sulfonate Group-containing vinyl chloride resin 12 parts [Nippon Zeon Co., Ltd., MR-110] Sodium sulfonate group-containing polyurethane resin 8 parts [Toyobo Co., Ltd., UR-8700] α-alumina (0.2 μm) 5 parts Carbon black (20 nm) 10 parts Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts Each of the resulting magnetic coating material for the uppermost layer and non-magnetic coating material for the lower layer, polyisocyanate compound (Coronate L 5 parts of Nippon Polyurethane Co., Ltd. was added.

(Examples 1 to 5 and Comparative Examples 1 to 3) The above-mentioned magnetic layer coating material containing the magnetic powder shown in Table 1,
And the above-mentioned non-magnetic layer coating material containing non-magnetic powder, which is applied on a polyethylene terephthalate film having a thickness of 10 μm by a wet-on-wet method, and then a magnetic field orientation treatment is performed while the coating film is undried. Then, after being dried, surface smoothing treatment is performed with a calendar (temperature is shown in Table 1), and Vickers hardness shown in Table 1 is obtained.
A magnetic layer having a thickness and a lower layer and an upper layer was formed.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene terephthalate film on the side opposite to the magnetic layer, the coating film is dried and calendered according to the above-mentioned calender temperature conditions. As a result, a back coat layer having a thickness of 0.8 μm was formed to obtain a wide original anti-magnetic tape.

Carbon black 40 parts (Raven 1035) Barium sulfate 10 parts (Average particle size 300 nm) Nitrocellulose 25 parts Polyurethane resin 25 parts [N-2301 manufactured by Nippon Polyurethane Co., Ltd.] Polyisocyanate compound 10 parts [Japan Polyurethane Manufactured by Coronate L] Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The raw anti-magnetic tape thus obtained was slit to _prepare an 8 mm wide magnetic recording medium for video having a surface roughness R _10Z of 18 nm. . The following evaluation tests were conducted on this magnetic recording medium. The results are shown in Table 1.

(Electrical characteristics (dB) RF output) 7 MHz by Sony 8 mm video camera CCDV-900
And the RF power at 10 MHz was measured.

(Running durability) Temperature 40 ° C., humidity 80% R
The repeated running durability in H was evaluated as follows.

A: No problem B: It runs, but the electrical characteristics are degraded by 2 dB or more. C: Travel stop

(Vickers hardness measurement method) Indenter shape: Triangle indenter 80 ° Load: 3 mg Pushing speed: 5 nm / sec Measurement environment: 23 ° C, 60% RH Indentation depth: Within 0.5 μm from the surface

(Same coefficient of friction) Head cylinder inlet,
Measure the tape tension at the exit

[0139]

[Equation 1] Was determined under the temperature and humidity conditions shown in Table 1.

(CN characteristic) The output level when a single wave of 7 or (10) MHz is recorded and the signal is reproduced, and 1M
The difference between the output of 6 MHz, which is lower by Hz, and (9 MHz) is Y-C.
The N ratio was used and expressed by comparison with the reference sample (Comparative Example 1).

[0141]

[Table 1]

[Brief description of drawings]

FIG. 1 is a diagram for explaining simultaneous multi-layer coating of magnetic layers by a wet-on-wet coating method.

FIG. 2 is a diagram of a coater head for applying a magnetic layer paint.

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-3-12025 (JP, A)                 JP 63-103429 (JP, A)                 JP-A-2-177125 (JP, A)                 JP-A-4-214215 (JP, A)                 Japanese Patent Laid-Open No. 7-176029 (JP, A)                 JP-A-2-260222 (JP, A)                 JP-A-4-295621 (JP, A)                 JP-A-4-330611 (JP, A)

Claims (4)

(57) [Claims] 1. A magnetic layer in which an upper layer and a lower layer are formed on a non-magnetic support, and the upper layer has magnetic powder dispersed in a binder.
A is, Vickers hardness of the magnetic layer is 40 or more, 20
Less than 0, the lower the Tsu nonmagnetic layer der containing nonmagnetic powder
Te, a magnetic recording medium Vickers hardness of the non-magnetic layer has a 30-100 der Rukoto. 2. The Vickers hardness of the upper layer is the non-magnetic
5 or more and 105 or less than the Vickers hardness of the lower layer containing powder
Magnetic recording according to claim 1, characterized in that it is high in the lower range.
Recording medium. 3. The film thickness of the upper magnetic layer is 0.1 μm or less.
The magnetic recording medium according to claim 1, having a thickness of less than 0.5 μm. 4. The lower layer containing the non-magnetic powder is in a wet state.
The upper layer is provided while being present.
The magnetic recording medium mounted.