JPH05298664A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium ensuring high C/N ratio and overwriting characteristics necessary for use as a digital recording medium and excellent in running durability at high temp. and humidity. CONSTITUTION:Plural layers are formed on a nonmagnetic substrate. The thickness of the uppermost magnetic layer is <=0.8mum, at least one of the layers contains an amine modified vinyl chloride copolymer and polyurethane having anionic functional groups as a binder and at least one layer other than the uppermost layer is a layer contg. nonmagnetic powder or a high permeability material.

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 that can obtain a high CN ratio and an overwrite characteristic required as a digital medium and that has excellent running durability under high temperature and high humidity.

[0002]

BACKGROUND OF THE INVENTION JP-A-3-80425 discloses a multilayer recording medium using an amine-modified vinyl chloride copolymer as a lower layer binder.

However, according to the research by the present inventor,
In the above technique, since the lower layer is the magnetic layer and the thickness of the uppermost magnetic layer is as thick as 1.0 μm or more, the film thickness loss and the self-demagnetization loss occur, and the high CN ratio and the overcurrent required for the digital medium are exceeded. The light characteristic was not obtained. Also, magnetic powder,
Since the binder is not sufficiently adsorbed by the filler such as non-magnetic powder, the physical properties of the coating film are not improved, and high temperature and high humidity (40 ° C, 80%
The running durability under RH) could not be sufficiently improved, and running stop due to puncture and increase in jitter were observed.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium which can obtain a high CN ratio and an overwrite characteristic required as a digital medium and which is excellent in running durability under high temperature and high humidity. ..

[0005]

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 following are included, and at least one layer of these layers contains an amine-modified vinyl chloride copolymer as a binder and polyurethane having a negative functional group, and at least one layer other than the uppermost layer is a non-magnetic powder or a high-permeability material. It is characterized in that it is a layer containing.

[0006]

DETAILED DESCRIPTION OF THE INVENTION In order to improve the CN ratio and overwrite characteristics, the thickness of the uppermost magnetic layer is preferably 0.8 μm or less, particularly preferably less than 0.5 μm, more preferably 0.1 to 0. It is 4 μm.

The amine-modified vinyl chloride copolymer has an amine or ammonium salt content of 0.001 to 1.0.
mmol / g is preferable, and more preferably 0.01 to
It is 0.2 mmol / g.

Further, as the negative functional group used in the polyurethane containing the negative functional group, --SO ₃ M, --OS
_{O 3 M, -COOM, -PO (} OM 1) 2, -OPO
(OM ¹ ) _{2 and the} like (M is a hydrogen atom or N
a represents an alkali metal such as K and Li, and M ¹ represents a hydrogen atom, an alkali metal such as Na, K and Li, or an alkyl group), and the preferable amount of the negative functional group is 0.0.
01-1.0 mmol / g, more preferably 0.005
~ 0.5 mmol / g. Especially 0.01-0.2m
Mol / g is preferred.

In the present invention, a vinyl chloride resin containing a cationic functional group such as an amine and a polyurethane resin containing an anionic functional group such as a sulfo group are used together in the same layer to obtain a magnetic powder or a non-magnetic material. It is considered that one of the reasons for the above improvement is that the binder is better adsorbed on the powder or the like and the coating film physical properties are improved. The above effect may not be obtained with a so-called betaine-type binder having an anionic functional group and a cationic functional group in one molecule.

The combined use of the amine-modified vinyl chloride-based copolymer and the polyurethane having a negative functional group described above results in a thicker lower layer than in the upper and lower layers, and has a large effect on the entire coating film. It is preferable to carry out, but it is more preferable to use them in combination in the upper and lower layers.

(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 is present between the magnetic layer and the non-magnetic support on the non-magnetic support. And are 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 electrification, and preventing transfer. Also, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

(Non-magnetic support) As a material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Examples of the cellulose derivative include plastics such as polyamide and 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 usually 3 to 1 in the case of a film or sheet.
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 back coat 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 a 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 thickness of the uppermost layer is 0.8 μm or less, preferably less than 0.5 μm, more preferably 0.1 to 0.5 μm.
It is 0.4 μm. By satisfying these conditions, the magnetic recording medium of the present invention can achieve the object of the present invention.

Ferromagnetic metal powders preferably used in the uppermost layer include Fe, Co, Fe--Al system, and Fe.
-Al-Ni system, Fe-Al-Zn system, Fe-Al-C
o type, Fe-Al-Ca type, Fe-Ni type, Fe-Ni
-Al system, Fe-Ni-Co system, Fe-Ni-Si-A
1-Mn type, Fe-Ni-Si-Al-Zn type, Fe-
Al-Si type, Fe-Ni-Zn type, Fe-Ni-Mn
System, Fe-Ni-Si system, Fe-Mn-Zn system, Fe-
Examples include ferromagnetic powders such as Co—Ni—P-based, Ni—Co-based, and metal magnetic powders containing Fe, Ni, Co, etc. as main components. 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, 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 has an average major axis length of 0.
Less than 25 μm, particularly 0.10 to 0.22 μm, more preferably 0.10 to 0.17 μm and a crystal size of 20.
It is preferably less than 0Å, particularly preferably 100 to 180Å. 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. Average major axis length and crystal size of ferromagnetic metal powder,
When the axial ratio is within the above range, the electromagnetic conversion characteristics can be further improved.

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

Further, the ferromagnetic powder preferably has a saturation magnetization amount (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.

Further, as a preferable structure of the ferromagnetic powder, the content ratio of Fe atoms and Al atoms contained in the ferromagnetic powder is Fe: Al = 100: 1 to 1 in terms of atomic number ratio.
The content ratio of Fe atoms and Al atoms existing in the surface region of 100: 20 or less at an analysis depth of ESCA of the ferromagnetic powder of 00:20 is Fe: Al = 30:
It has a structure of 70 to 70:30. Alternatively, Fe atoms, Ni atoms, Al atoms, and Si atoms are contained in the ferromagnetic powder, at least one of Zn atoms and Mn atoms is further contained in the ferromagnetic powder, and the content of Fe atoms is 90 atomic%. As described above, the content of Ni atoms is 1 atom% or more and less than 10 atom%, and the content of Al atoms is 0.1 atom%.
Above, less than 5 atomic%, and the content of Si atoms is 0.1 atomic%.
Or more and less than 5 atomic%, the content of Zn atoms and / or the content of Mn atoms (however, when both Zn atoms and Mn atoms are contained, this total amount) is 0.1 atomic% or more, 5
Fe atoms and N present in the surface region of less than 100 Å or less in ESCA analysis depth of the ferromagnetic powder
The content ratio of i atom, Al atom, Si atom, Zn atom and / or Mn atom is Fe: Ni: Al: S in terms of atomic number ratio.
i (Zn and / or Mn) = 100: (4 or less):
(10-60): (10-70): (20-80) The ferromagnetic powder etc. which have a structure are mentioned.

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, see IEEE T
trans, on MAG-18 16 (1982).

In the present invention, 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 of Ba-ferrite powder in which a part of Fe is replaced by at least Co and Zn (diagonal length of plate surface of hexagonal ferrite) 400-
900Å, plate ratio (value obtained by dividing length of diagonal line of plate surface of hexagonal ferrite by 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 substituting Fe with Co, and further by partially substituting with Zn, it is not possible to obtain it 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, 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. _{BaOn ((Fe 1-m M} m) 2 O 3) [ provided that, m> 0.36 (However, 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 size 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 preferably has a saturation magnetization (σs), which is a magnetic characteristic, usually 50 emu / g or more. If the saturation magnetization is less than 50 emu / g, the electromagnetic conversion characteristics may deteriorate.

As a preferable specific example of the Ba-ferrite used in the present invention, Co-substituted Ba ferrite can be mentioned.

As a method for producing the hexagonal magnetic powder, for example, oxides and carbonates of each element necessary for forming the desired Ba-ferrite are used together with a glass-forming substance such as boric acid. Melting, quenching the obtained melt to form glass, then heat treating this glass at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally removing the glass component by heat treatment. In addition to the glass crystallization method, 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 99% by weight, and particularly preferably 75 to 99% by weight. 90% by weight.

By the way, in the layers other than the uppermost magnetic layer and containing the non-magnetic powder, the thickness of the magnetic layer is 0.8 μm or less, so that the uppermost magnetic layer is replenished with a lubricant. 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.

[Layer containing non-magnetic powder or layer containing high-permeability material other than the 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, 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, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide ,
Examples thereof include titanium carbide, tripoly, diatomaceous earth, dolomite, and polymer powder such as polyethylene.

Of these, preferred are carbon black, CaCO ₃ , titanium oxide, barium sulfate and α-.
Examples thereof include inorganic powders such as Al ₂ O ₃ and α-iron oxide, and polymer powders such as polyethylene.

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, because the non-magnetic powder in the non-magnetic layer does not adversely affect the surface properties of the magnetic layer.

The content of the non-magnetic powder in the non-magnetic layer is 5 to 99% by weight, preferably 60 to 95% by weight, particularly preferably 75 to 100% by weight based on the total amount of all components constituting the nonmagnetic layer. It is 95% by weight. When the content of the non-magnetic powder is within the above range, the state of the surface of the uppermost layer composed of the magnetic layer can be improved.

(High Permeability Material) This high permeability material has a coercive force Hc of 0 <Hc ≦ 1.0 × 10 ⁴ [A /
m], preferably 0 <Hc ≦ 5.0 × 10 ³ [A / m]
Is. 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, as the high magnetic permeability material,
It is preferable to appropriately select a material within the range of the coercive force. Examples of such a high magnetic permeability material include a metal soft magnetic material and an oxide soft magnetic material. Examples of the soft metal magnetic material include Fe—Si alloys and Fe—Al alloys (Alperm, Alfemol,
Alfer), permalloy (Ni-Fe binary alloy, and multi-component alloy in which Mo, Cu, Cr, etc. are added), sendust (Fe-Si-Al [9.6 wt% Si, 5.4%) Of Al and the rest is Fe]), F
An e-Co alloy etc. can be mentioned. 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. High permeability materials are
One of them may be used alone, or two or more thereof may be used in combination.

As the soft oxide 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 to 300.
nm, preferably 1 to 100 nm, particularly preferably 1 to
It is preferably 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 usually 5 to 99% by weight, preferably 50 to 95% by weight, more preferably 60 to 95% by weight.
% 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 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, pigments such as metal oxides such as zinc oxide, barium nitrate and titanium oxide, tin oxide film, or conductive material such as antimony solid solution oxide film There are some that have been coated with.

(Binder) The uppermost magnetic layer and /
Or The binder used to form the layers other than the magnetic layer, said polyurethane having amine-modified vinyl chloride copolymer and negative functional groups is used, the polyurethane resin is -SO ₃ having a negative functional group M, -OSO
₃ M, -COOM and -PO (OM ¹⁾ _2, -OPO
It is preferable to include a repeating unit having at least one polar group selected from (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 atom such as Na, K and Li, or an alkyl group.

The amine-modified vinyl chloride-based copolymer of the present invention can be easily synthesized by a known method.

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 a single type, and two or more types can be used in combination. The weight ratio of the polyurethane of the present invention to the vinyl chloride resin of the present invention is usually preferably 90:10 to 10:90, more preferably 70:30 to 30:70, and particularly 70: It is in the range of 30 to 50:50.

Next, the polyurethane of the present invention will be described.

This 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, when a polyester polyol having a negative functional group is used as a raw material, a polyurethane having a negative functional 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 negative functional group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a negative functional group and a chlorine atom is also effective.

Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH
_{2 CH 2 OSO 2 M, Cl} -CH 2 COOM, Cl-C
H ₂ -P (= 0) (OM ¹ ) _{2 As} a technique for introducing a negative functional group into polyurethane, JP-B-58-41565 and JP-A-57-92 are known.
No. 422, No. 57-92423, No. 59-8127.
No. 59, No. 5423, No. 59-5424, No. 62
No. 121923, etc., 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, it is desirable to add polyisocyanate to 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 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 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, more preferably 30:70 to 70:30. Is.

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 is manufactured according to a known method used for manufacturing a single-layer or multi-layer structure type magnetic recording medium. can do.

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.

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

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 dispersers, 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 a wet-on-wet multi-layer coating method 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 composed of 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 paint 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).

As the coater head, the head shown in FIG. 2C 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 this wet-on-wet multi-layer coating, since the upper magnetic layer is applied 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 smooth. 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 blended in the above paint or a diluent solvent when applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone: alcohols such as methanol, ethanol, propanol, butanol: methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol senoacetate: 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 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 above temperature is usually 50 to 120 ° 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 value is out of the range, it may be difficult or impossible to specify the surface condition of the magnetic layer as in the present invention.

[0098]

According to the present invention, a high CN ratio and an overwrite characteristic required for a digital medium can be obtained, and a magnetic recording medium having high running durability under high temperature and high humidity can be obtained, and a running stop due to puncture can be obtained. No increase in jitter is observed.

[0099]

EXAMPLES Examples of the present invention will be described below.

The following components, ratios, and operation order can be variously changed 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.

[Coating A for Upper Layer] Fe—Al-based ferromagnetic metal powder (Fe: Al weight ratio = 100: 8, average major axis length: 0.16 μm, Hc: 1580 Oe, σs: 120 emu / g, axial ratio 8, the crystallite size: 170 Å) 100 parts of an amine-modified vinyl chloride-based resin _{^{(-N + (CH 3) 3}} Cl - 0.03mmol / g) 10 parts of sulfonic acid metal salt-containing polyester polyurethane resin (SO ₃ M concentration of 0. 08 mmol / g) 5 parts Alumina (α-Al ₂ O ₃ , average particle size: 0.2 μm) 3 parts Carbon black (average particle size 40 nm) 1 part Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

[Upper Layer Coating Material B] F in Upper Layer Coating Material A
Instead of the e-Al-based ferromagnetic metal powder, Co-substituted barium ferrite (Hc: 1100 Oe, BET 45 m ² /
g, σs: 64 emu / g, the same as A except that the plate ratio 4) was used.

[Lower layer coating C] TiO ₂ (average particle size 30 nm) 90 parts Carbon black (average particle size 20 nm) 10 parts Amine-modified vinyl chloride resin (-N ⁺ (CH ₃ ) ₃ Cl ^- 0.03 mmol / g) 6 parts Polyester polyurethane resin containing sulfonic acid metal salt (SO ₃ M concentration 0.04 mmol / g) 3 parts Alumina (α-Al ₂ O ₃ , average particle size: 0.2 μm) 3 parts Myristic acid 1 part Butyl Stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

[Lower layer paint D] In lower layer paint C, T
Same as C except that Fe—Si—Al sendust alloy powder (coercive force Hc = 40 A / m, μi = 200 H / m, particle size 50 nm) was used instead of iO ₂ .

[Upper layer coating materials E and F] [Lower layer coating materials G and H] In the coating materials A, B, C and D, except that the vinyl chloride resin containing a sulfonic acid metal salt is used instead of the amine-modified vinyl chloride resin. Is the same as A, B, C and D.

[Lower layer coating material I] In coating material C, TiO ₂
Instead of 90 parts, Co-γFe ₂ O ₃ (average particle size 0.16 μm, crystallite size 330Å, Hc: 800
Oe, σs: 78 emu / g) The same except that 90 parts were used.

Next, 5 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the obtained magnetic coating material for upper layer and coating material for lower layer, and polyethylene of 10 μm thickness was prepared by wet-on-wet method. After coating on a terephthalate film, magnetic field orientation treatment is carried out while the coating film is still undried, followed by drying and then surface smoothing treatment with a calender, a lower layer having a thickness of 2.0 μm and a thickness of 0. A magnetic layer consisting of an upper layer of 3 μm was formed.

Further, a coating material having the following composition is applied to the surface (rear surface) of the polyethylene phthalate film on the side opposite to the magnetic layer, the coating film is dried and calendered to give a thickness of 0. A back coat layer having a thickness of 8 μm was formed to obtain a wide original anti-magnetic tape.

[Backcoat layer coating material] Carbon black (Raven 1035) 40 parts Barium sulfate (average particle size 300 mμ) 10 parts Nitrocellulose 25 parts Polyurethane resin (N-2301 manufactured by Nippon Polyurethane Co.) 25 parts Polyisocyanate compound (Nippon Polyurethane Co., Coronate L) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts

The original fabric thus obtained is slit to 8 m.
An m-video tape was created. C of this video tape
The N characteristic, the overwrite characteristic and the running durability were measured as follows. The results are shown in Table 1.

(CN characteristic) A single wave of 9 MHz was recorded,
The output level when the signal was reproduced was expressed by comparison with the reference sample (Comparative Example 1).

(Overwrite characteristic) A residual output level of a 2 MHz signal was recorded when a 2 MHz signal was recorded at a saturation level and then a 9 MHz signal was (overwritten) recorded. The lower the residual output level, the better the overwrite characteristic.

(Running durability under high temperature and high humidity (40 ° C., 80% RH)) S-550 under the environment of 40 ° C., 80% RH
(Manufactured by Sony Corporation) was used to run the tape for 50 passes, and the jitter value after 50 passes was measured. VTR jitter meter (M
K-6124) (measurement unit: μ
s).

Further, the tape stop due to fluttering while the tape was running was also measured.

[0116]

[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.

Claims (1)

[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 an amine-modified vinyl chloride is used as a binder for at least one of those layers. A magnetic recording medium comprising a system copolymer and polyurethane having a negative functional group, wherein at least one layer other than the uppermost layer is a layer containing a non-magnetic powder or a high magnetic permeability material.