JP3333966B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic card.

[0002]

2. Description of the Related Art In recent years, there has been a demand for higher density and higher performance of magnetic recording media.

[0003] As the prior art mainly in the extrusion method for the purpose of producing a magnetic recording medium, those described in JP-A-57-8477, JP-A-58-104666, and JP-A-60-238179 are known. ing. As a conventional example of the overlay and the coating method using an extrusion coater, a sequential multilayer coating method described in JP-A-64-288364, and JP-A-2-25265, JP-A-2-26862, the simultaneous multilayer There is a description of the coating method.

The multilayer structure of hexagonal magnetic powder and acicular magnetic powder is described in JP-A-1-128228.

Japanese Patent Application Laid-Open Nos. 60-125927 and 60-125927 disclose examples of providing a layer containing non-magnetic particles between a support and a magnetic layer.
No. 1-296525, the 62-121927 JP, Kokoku 1-20488 Patent such as carbon black, in JP 59-142741, examples of SnO _2, the JP-63-187418, the practice of red iron oxide Examples are allowed.

Further, by providing a plurality of magnetic layers and defining the glass transition point (Tg) of the polyurethane resin contained as a binder used in the upper layer and the lower layer, electromagnetic conversion characteristics, still durability and running durability are improved. The technology to make it possible has been disclosed (JP-A-2-105326, JP-A-2-227823, JP-A-3-2168).
No. 12).

However, with the trend toward higher density of magnetic recording, the recording method is changing from the analog recording method to the digital recording method. Digital recording methods are being adopted for audio recording and video recording, but the recording medium currently used is an analog medium and is not always optimal as a digital recording medium.

That is, in the conventional medium configuration, for a digital recording medium, the thickness of the uppermost magnetic layer is as thick as 0.5 μm or more, and in short-wavelength recording, a decrease in output due to reproduction demagnetization due to a loss in medium thickness is caused. And there are drawbacks such as poor signal overwriting characteristics.

Further, since a magnetic layer is used as a lower layer, self-demagnetization occurs, and a high CN ratio cannot be obtained. Low head temperature (0 ° C), low humidity (40 ° C, 20%
RH), there was a problem such as a decrease in RF output.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having high-frequency electromagnetic conversion characteristics suitable for high-density digital recording, good signal overwriting characteristics, and excellent durability. It is to provide a recording medium.

[0011]

The object of the present invention is to provide a nonmagnetic support having a glass transition point (Tg) as a nonmagnetic powder and a binder.
A nonmagnetic layer containing a polyurethane resin at −40 ° C. to 0 ° C.,
The film thickness is 0.2 μm or more and less than 0.5 μm, and as a binder
Magnetic layer containing polyurethane resin with Tg of 0 ° C to 100 ° C
Are formed in this order by a magnetic recording medium.

In a preferred embodiment, a polyurethane resin having a glass transition point (Tg) of 0 ° C. to 40 ° C. is used as the binder of the uppermost layer in order to improve the head clog characteristics at a low temperature (0 ° C.). More preferably, low humidity (40 ° C, 20
% RH), it is more preferable to use a polyurethane resin having a glass transition point (Tg) of 40 ° C to 100 ° C as the binder of the uppermost layer.

[0013] will be described briefly here for the polyurethane resin used in the magnetic layer according to claim 1, but details
It will be described later .

[0014] Polyurethane resins of the present invention has a glass transition point (Tg) in Focusing molecules bone price, is obtained by adjusting the polymerization degree, further polar groups for characteristic adjusting, introducing a functional group that forms an intramolecular salt Modified polyurethane resin may be used.

-Measurement method of the above glass transition point (Tg)-As a measuring device, a sample having a thickness of 30 μm, a width of 10 mm and a length of 25 mm was measured using Vibron DDV-II-EA (manufactured by Toyo Baldwin Co., Ltd.). While heating at 5 ° C / min in the range of 100 ° C to + 100 ° C, a sine wave stretching strain with a frequency of 10Hz is given to the edge in the width direction, and the maximum tanδ of the phase difference δ of both vectors of the sine wave stress appearing at the other end Is given as Tg.

The purpose of the polyurethane resin in the present invention can be sufficiently achieved by the distribution of the glass transition point (Tg) of the ordinary polyurethane resin.

Hereinafter, the magnetic recording medium of the present invention will be described in detail.

-Non-magnetic support-Materials for forming the non-magnetic support include, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate and the like. mention may be made of cellulose derivatives, polyamide, plastic such as polycarbonate.

The form of the nonmagnetic support is not particularly limited, and may be mainly a tape, a film, a sheet, a card,
Disc-shaped, drum-shaped, etc.

The thickness of the non-magnetic support is not particularly limited.
The thickness is 100 μm, preferably 5 to 50 μm, and is appropriately selected according to a recorder or the like in the case of a disk or a card, and about 30 μm to 10 mm in the case of a drum.

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

A back coat layer is provided on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the running properties of the magnetic recording medium, preventing charge and preventing transfer. Preferably, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

[0023] - Magnetic layer - In the present invention, the magnetic layer is the uppermost layer. This magnetic layer is basically made by dispersing magnetic powder in a binder resin.

The uppermost magnetic layer preferably contains a ferromagnetic metal powder and / or a hexagonal magnetic powder.
The thickness of the uppermost layer is 0.2 μm or more and less than 0.5 μm, preferably 0.2 to 0.4 μm. By satisfying these conditions, the magnetic recording medium of the present invention
High frequency electromagnetic conversion characteristics can be improved.

The ferromagnetic metal powder used for the uppermost layer includes Fe, Co, Fe-Al, Fe-Al-Ni, and Fe-Al-Zn.
System, Fe-Al-Co system, Fe-Al-Ca system, Fe-Ni-Al system, Fe-Ni-Co
System, Fe-Ni-Si-Al-Mn system, Fe-Ni-Si-Al-Zn system, Fe-Al-Si
System, Fe-Ni-Zn system, Fe-Ni-Mn system, Fe-Ni-Si system, Fe-Mn-Zn
, Fe-Co-Ni-P, Ni-Co, ferromagnetic powders such as metal magnetic powders mainly composed of Fe, Ni, Co and the like. Among them Fe
Metal powder has excellent electrical properties.

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

Particularly, the ferromagnetic metal powder preferred for the purpose of the present invention is a metal magnetic powder containing iron as a main component, and is preferably Al or Al.
And Ca, Al: Fe: Al = 100: 0.5 ~
100: 20, Ca: Fe: Ca = 100: 0.1 to 10 by weight
It is desirable to contain in the range of 0:10.

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, the electromagnetic conversion characteristics are improved and the dropout is reduced. Can be done.

It is not clear why the electromagnetic conversion characteristics are improved or the dropout is reduced. However, it is considered that the coercive force is increased and the aggregates are reduced due to the improved dispersibility.

The ferromagnetic metal powder used in the present invention has an average major axis length of 0.30 observed with a transmission electron microscope.
μm, preferably 0.10 to 0.22 μm, more preferably 0.1 μm.
10-0.17μm and the crystal size by X-ray diffraction method is 200
It is preferable that the angle is less than 100, especially 100 to 180 °. 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 preferably has a coercive force (Hc) in the range of usually 600 to 5,000 Oe. If the coercive force is less than 600 Oe, the electromagnetic conversion characteristics may deteriorate, and
If it exceeds 5,000 Oe, recording may not be possible with a normal head, which is not preferable.

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

Further, in the present invention, the specific surface area by the BET method is 30 m ² / g or more, particularly
A ferromagnetic metal powder of 45 m ² / g or more is preferably used.

A preferred specific example of the ferromagnetic metal powder used in the present invention is a Fe—Al ferromagnetic metal powder (Fe: Al
Weight ratio = 100: 5, average major axis length 0.16 μm, Hc: 1580 Oe,
σ _s : 120 emu / g).

Further, the preferred structure of the ferromagnetic metal powder is such that Fe atoms contained in the ferromagnetic metal powder and Al
Fe: Al = 100: 1 to 100:
20 and the content ratio between Fe atoms and Al atoms existing in a surface area of 100 ° or less at an analysis depth by ESCA of the ferromagnetic metal powder is Fe: Al = 30: 70 to 70:30 in atomic ratio. Having the following structure. Alternatively, Fe, Ni, Al, and Si atoms are contained in the ferromagnetic metal powder, and at least one of Zn atoms and Mn atoms is contained in the ferromagnetic metal powder, and the content of Fe atoms is reduced. 90 atom% or more, Ni atom content is 1 atom% or more, less than 10 atom%, Al atom content is 0.1
Atomic% or more and less than 5 atomic%, the content of Si atom is 0.1 atomic% or more and less than 5 atomic%, the content of Zn atom and / or the content of Mn atom (however, both Zn atom and Mn atom are The total amount of the ferromagnetic metal powder is 0.1 atomic% or more and less than 5 atomic%.
Fe atoms, Ni atoms, Al atoms and S existing in the surface area of 100 ° or less
The content ratio of i atom to Zn atom and / or Mn atom is atomic ratio: Fe: Ni: Si (Zn and / or Mn) = 100: (4 or less) :( 1
0-60): (10-70): ferromagnetic metal powder having a structure of (20-80).

In the magnetic layer of the uppermost layer of the magnetic recording medium of the present invention, hexagonal magnetic powder can be used as the magnetic powder.

As the hexagonal magnetic powder, there are, for example, barium ferrite and strotium ferrite. In the present invention, Ba-ferrite, whose electromagnetic properties are easily adjusted, is mainly used.

The preferred hexagonal Ba-ferrite powder includes an average particle size (diagonal length of the hexagonal ferrite plate surface) of Ba-ferrite powder in which at least a part of Fe is replaced by Co and Zn. Å900Å, plate ratio (value obtained by dividing the diagonal length of the plate surface of hexagonal ferrite by the plate thickness)
0, more preferably 2.0 to 6.0, coercive force (Hc) 450 to 1500
Ba-ferrite.

In the Ba-ferrite powder, the coercive force is controlled to an appropriate value by partially substituting Fe with Co. Further, by partially substituting Zn, a high coercive force that cannot be obtained only by Co substitution is obtained. It is possible to obtain a magnetic recording medium which realizes a 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 electromagnetic conversion characteristics. Further, Ba- used in the present invention
Ferrite has a part of Fe, Ti, In, Mn, Cu, Ge,
It may be substituted with a transition metal such as Sn.

The Ba-ferrite used in the present invention is represented by the following general formula.

BaO · n ((Fe _1-mm M _m ) ₂ O ₃ ) [However, 0.36 <m <1 (however, Co + Zn = 0.08 to 0.3, C
o / Zn = 0.5 to 10), n is 5.4 to 11.0, preferably 5.4 to 6.0, M is a substituted metal, and the magnetic number is a combination of two or more elements whose average number is 3. Particles are preferred. In the present invention, the average particle size of Ba-ferrite, plate ratio,
The reason why it is preferable that the coercive force is within the above range is as follows. That is, the average particle diameter of the Ba-ferrite is preferably 300 ° or more in order to obtain a sufficient amphoteric output when used as a magnetic recording medium. In order to improve the surface smoothness and reduce the noise level, 900 ° C. It is preferred that: By setting the plate ratio to 2.0 or more, a perpendicular orientation ratio suitable for high-density recording can be obtained when a magnetic recording medium is used, and the plate ratio is improved to improve surface smoothness and reduce noise level. It is preferably 10.0 or less.
Further, the coercive force is preferably 450 Oe or more for holding the recording signal, and the coercive force is preferably 1500 Oe or less to prevent the head from being saturated.

The barium ferrite magnetic powder used in the present invention usually has a saturation magnetization (σ _s ) as a magnetic property of 50 e.
It is desirable to be mu / g or more. This saturation magnetization is 50em
If the ratio is less than u / g, the electromagnetic conversion characteristics may be deteriorated.

Further, according to the present invention, according to the increase in the recording density, the Ba-type having a specific surface area of 30 m ² / g or more by the BET method is used.
It is desirable to use ferrite magnetic powder.

As a method for producing the hexagonal magnetic powder used in the present invention, for example, oxides and carbonates of each element necessary for forming a target Ba-ferrite are prepared by
For example, it is melted together with a glass-forming substance such as boric acid, and the obtained melt is quenched to form a glass. In addition to the glass crystallization method of finally removing the glass component by heat treatment, a coprecipitation-calcination method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method, or the like can be applied.

The content of the ferromagnetic powder and / or the hexagonal magnetic powder in the magnetic layer is usually 50 to 99% by weight, preferably 60 to 99% by weight.

The layers containing non-magnetic powder other than the uppermost magnetic layer have a thickness of less than 0.5 μm, so that the lubricant is supplied to the uppermost magnetic layer. Functions as a layer. In order for the layer below the magnetic layer to function well as a lubricant replenishment layer, the nonmagnetic powder contained in the layer below the magnetic layer preferably has as little oil absorption as possible, usually 200 ml / 100 g or less. , Preferably 10
0ml / 100g or less.

The non-magnetic powder which may be contained in the non-magnetic layer is
These are listed below.

As the non-magnetic powder, those having the above characteristics can be appropriately selected from various known non-magnetic powders used for this type of magnetic recording medium. Examples of the non-magnetic powder include carbon black, graphite, titanium oxide, barium sulfate, ZnS, M
gCO ₃ , CaCO ₃ , ZnO, CaO, tungsten dioxide, molybdenum dioxide, boron 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, quartzite,
Silicon nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, triboli,
Diatomaceous earth, dolomite and the like can be mentioned. Among these, carbon black, CaCo ₃ ,
It is an inorganic powder such as titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-iron oxide, or a polymer powder such as polyethylene.

The particle diameter of the nonmagnetic powder is usually 1 to 300 nm, preferably 1 to 100 nm, in order to improve the surface properties of the lower layer.
nm, more preferably 1 to 50 nm.

[0050] The following may be high permeability material is contained in at least one layer other than the uppermost layer, it is described here.

The high magnetic 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). When the coercive force is within the above range, the effect of stabilizing the magnetization region of the uppermost layer as a high magnetic permeability material is exhibited. When the coercive force is in the above range, characteristics as a magnetic material are exhibited, which is preferable.

[0052] As high-permeability material, it is preferable to select a material which is within the range of the coercive force appropriately, as such a high-permeability material, for example, metallic soft-magnetic material,
An oxide soft magnetic material can be used.

As the metal soft magnetic material, Fe-Si alloy, Fe-Al alloy (Alperm, Alfenol, Alfer), permalloy (Ni-Fe type binary alloy, and Mo, Cu, Cr, etc. were added thereto. Multi-component alloys), sendust (Fe-Si-Al [9.6% by weight of Si, 5.4% of Al, composition with the balance being Fe]), and Fe-Co alloys. Among these, Sendust is preferred as a preferred metal soft magnetic material. In addition,
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. One of the high magnetic permeability materials can be used alone, or two or more thereof can be used in combination.

The oxide soft magnetic materials include spinel-type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ , CoFe ₂ O ₄ and NiFe _{2
O 4, MgFe 2 O 4,} Li 0.5 Fe 2.5 O 4 and, Mn-Zn ferrite, N
Examples thereof include i-Zn ferrite, Ni-Cu ferrite, Cu-Zn ferrite, Mg-Zn ferrite, and Li-Zn ferrite. Among these, Mn-Zn ferrite and Ni-Zn ferrite are preferable. These oxide soft magnetic materials may be used alone or in combination of two or more.

The high-permeability material has a particle size of 1 nm to 300 nm, particularly 1 nm to 100 nm, and more preferably 1 nm to 50 nm, in order to improve the surface properties of the layer below the uppermost layer . In order to obtain such fine powder, a soft metal magnetic material can be obtained by spraying a molten alloy under a vacuum atmosphere. In addition, the oxide soft magnetic material can be made into 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 50 to 99% by weight, preferably 60 to 95% by weight, and more preferably 75 to 95% by weight.
When the content of the high magnetic permeability material is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained. When the high magnetic permeability material is 50% by weight or more, the effect as a high magnetic permeability layer is obtained, which is preferable.

The layer containing the high magnetic permeability material includes
It may contain the above-mentioned nonmagnetic powder.

The above non-magnetic powder or high magnetic permeability material usually has an average particle size of 1 to 300 nm, preferably 1 to 100 nm.
More preferably, it is 1 to 50 nm.

-Binder (Binder)-The binder (binder) used to form the uppermost magnetic layer and the layers other than the magnetic layer will be described in detail.

[0060] As the binder used in the magnetic layer and the nonmagnetic layer of the present invention, port Riureta emissions are those typical, these resins are _{-SO 3 M, -OSO 3 M,} -COOM and -PO (OM ¹ ) ₂
It is preferable to include a repeating unit having at least one polar group selected from Also polyester, chloride
Vinyl chloride resins such as vinyl copolymers and the like;
-SO ₃ M in the resin, -OSO ₃ M, selected from -COOM and -PO (OM ¹⁾ ₂
A repeating unit having at least one polar group
What is included may be additionally used.

[0061] However, in the polar group, M represents a hydrogen atom or Na, K, an alkaline metal such as Li.

The polar group has an effect of improving the dispersibility of the ferromagnetic powder, and the content in each resin is 0.1 to 8.0 mol%.
Preferably it is 0.5-6.0 mol%. When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is reduced, and when the content is more than 8.0 mol%, the magnetic paint tends to gel. The weight average molecular weight of each resin is 15,000
A range of ~ 50,000 is preferred.

The content of the binder in the magnetic layer is usually 10 to 40 parts by weight, preferably 15 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

The 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 90:10 by weight. 1010: 90, preferably in the range of 70:30 to 30:70.

The vinyl chloride copolymer containing a polar group is synthesized by an addition reaction of a copolymer having a hydroxyl group, such as a vinyl chloride-vinyl alcohol copolymer, with a compound having the following polar group and chlorine atom. Can be.

Cl—CH ₂ CH ₂ SO ₃ M, Cl—CH ₂ CH ₂ OSO ₃ M, Cl—CH ₂ COOM, Cl—CH ₂ —P (= O) (O M) ₂ where M is a hydrogen atom Or alkali such as Na, K, Li, etc.
Represents a metal. Taken from these compounds _{Cl-CH 2 CH 2 SO 3} Na Examples, describing the addition reaction, as follows.

-(CH ₂ C (OH) H)-+ Cl-CH ₂ CH ₂ SO ₃ Na →-(CH ₂ C (OCH ₂ CH ₂ SO ₃ Na) H)- The system 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, and using a general polymerization initiator such as BPO (benzoyl peroxide), It can be obtained by performing a polymerization reaction using a radical polymerization initiator such as AIBN (azobisisobutyronitrile), a redox polymerization initiator, a cationic polymerization initiator, or the like.

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

When a carboxylic acid or a salt thereof is introduced, 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 may be used.

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

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 a monomer for introducing an epoxy group, for example, glycidyl acrylate is preferable.

Regarding the technique for introducing a polar group into a vinyl chloride copolymer, see, for example, JP-A-57-44227 and JP-A-58-1.
08052, 59-8127, 60-101161, 60-235814
No. 60-238306, No. 60-238371, No. 62-121923,
Nos. 62-146432, 62-146433, etc.
These can also be used in the present invention.

[0073] Next, described for the synthesis of the port Riesuteru resin and polyurethane resin.

Generally, a polyester resin is obtained by reacting a polyol with a polybasic acid.

Using the known method, a polyester (polyol) having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group.

Examples of polybasic acids having a polar group include:
Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfophthalic acid Contact and their sodium salts, and potassium salts.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, , 6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like.

Incidentally, a polyester having another polar group introduced therein can also be synthesized by a known method.

Next, the polyurethane resin will be described.

This is obtained from the reaction of a polyol with a polyisocyanate.

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 resin having a polar group can be synthesized.

Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI), hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalenediisocyanate (NDI), and tolidine diisocyanate (TOD).
I), lysine isocyanate methyl ester (LDI)
And the like.

As another method for synthesizing a polyurethane resin having a polar group, an addition reaction of a polyurethane having a hydroxyl group with 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 OSO ₂ M, Cl—CH ₂ COOM, Cl—CH ₂ —P (= O) (O M) ₂ where M is a hydrogen atom Or alkali such as Na, K, Li, etc.
Represents a metal. Incidentally, as a technique for introducing a polar group into the polyurethane, for example, JP-B-58-41565, JP-A-57-9
No. 2422, No. 57-92423, No. 59-8127, No. 59-5423, No.
It is described in publications such as 59-5424 and 62-121923, and these can also 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 of the total binder.

As the resin, for example, a resin having a weight average molecular weight
10,000-200,000 vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose Styrene-butadiene copolymer, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin,
Various synthetic rubber-based resins are exemplified.

-Other Components- In the present invention, in order to improve the quality of the magnetic layer, additives such as a durability improver, a dispersant, an abrasive, an antistatic agent and a filler are contained as other components. Can be.

Examples of the durability improver include polyisocyanates.
For example, aromatic polyisocyanate such as an adduct of tolylene diisocyanate (TDI) or the like and an active hydrogen compound;
There is an aliphatic polyisocyanate such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid;
Salts of these alkali metals or salts of alkaline earth metals or amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefin oxyquaternary ammonium salts; azo compounds having a carboxyl group and a sulfonic acid group. Can be mentioned. 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. The amount of addition
If the content is less than 0.2% by weight, the running property tends to decrease, and
When the content is more than 10% by weight, fatty acids are likely to exude to the surface of the magnetic layer and output is liable to decrease.

Further, the amount of the fatty acid ester to be 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 tends to deteriorate, and if it exceeds 10% by weight, the fatty acid ester easily exudes to the surface of the magnetic layer or the output tends to decrease.

When it is desired to further enhance the lubricating effect by using a fatty acid and a fatty acid ester in combination, the weight ratio of the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, and 12 to 22 carbon atoms.
Is more preferable.

Specific examples of fatty acids 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,
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 palmate 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- Utyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmate, isopentyl stearate, diethylene glycol mono-butyl ether palminate, diethylene glycol mono- Butyl ether palmitate and the like.

Further, as a 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 also be used.

Next, as a specific example of the abrasive, for example, α
-Aluminum, fused alumina, chromium oxide, titanium oxide, α-
Iron oxide, silicon oxide, silicon nitride, tungsten carbide,
Molybdenum carbide, boron carbide, corundum, zinc oxide,
Cerium oxide, magnesium oxide, boron nitride, and the like can be given. As an abrasive, the average particle size is 0.05 to 0.6 μm
Is preferred, and more preferably 0.1 to 0.3 μm.

As the antistatic agent, carbon black,
Conductive powders such as graphite; cationic surfactants such as quaternary amines; anionic surfactants containing acid groups such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid;
Examples include amphoteric surfactants such as aminosulfonic acid; and natural surfactants such as saponin. The aforementioned antistatic agent is usually added in the range of 0.01 to 40% by weight based on the binder.

-Manufacture of Magnetic Recording Medium- In the magnetic recording medium of the present invention, the magnetic layer is preferably applied by a so-called wet-on-wet method in which the lower layer is in a wet state. As the wet-on-wet method, a method used for manufacturing a known multilayer structure type magnetic recording medium can be appropriately adopted.

For example, generally, a ferromagnetic metal powder or a hexagonal plate-like powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent and the like are kneaded with a solvent to prepare a high-concentration magnetic paint. Then, after the high-concentration magnetic paint is diluted to prepare a magnetic paint, the magnetic paint is applied to the surface of the non-magnetic support.

Examples of the solvent include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIB
K) ketones such as cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate; cyclic ethers such as tetrahydrofuran;
Halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

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

Examples of the kneading and 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,
Examples include a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the above kneading and dispersing machines, kneading and dispersing machines capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 kg of magnetic powder) include a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill. is there.

To coat, for example, a layer containing the high magnetic permeability material of the present invention and a magnetic layer on a non-magnetic support, specifically, as shown in FIG. Each coating material for the magnetic layer is applied in a wet-on-wet manner on the support 1 in the form of a wet-on-wet method using extrusion coaters 10 and 11, and then passed through a magnet 33 for orientation or a magnet 33 for vertical orientation. Introduced in 34, hot air is blown from nozzles arranged above and below to dry. Next, the dried support 1 with each coating layer is guided to a super calendar device 37 composed of a combination of calendar rolls 38, where it is calendered, and then wound up on a take-up roll 39. The magnetic film thus obtained is 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 may be supplied to the extrusion coaters 10 and 11 through an in-line mixer (not shown). Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coaters 10 and 11 are provided with liquid reservoirs 13 and 14, respectively, and paints from each coater are overlapped in a wet-on-wet manner. That is, immediately after the application of the lower layer paint (when it is in an undried state), the upper magnetic layer paint is applied in multiple layers.

The coater head is shown in FIG.
(B) and (c) are shown, but the head of (c) is preferable in the present invention.

Examples of the solvent to be blended in the above coating material or a diluting solvent for coating this coating material include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; Esters such as methyl, 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 And halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene. These various solvents can be used alone, or two or more of them can be used in combination.

The magnetic field of the oriented magnet or the magnet for vertical orientation is about 20 to 5,000 gauss, the drying temperature of the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 gauss.
About a minute.

In the wet-on-wet method, a combination of a reverse roll and an extrusion coater is used.
A combination of a gravure roll and an extrusion coater can also be used. Furthermore, an air doctor coater,
Blade coater, air knife coater, squeeze coater,
Impregnation coater, transfer roll coater, kiss coater,
A cast coater, a spray coater and the like can be combined.

In the multi-layer coating in the wet-on-wet method, the upper magnetic layer is coated while the layer located below the uppermost layer is kept wet, so that the surface of the lower layer (that is, the uppermost layer is Interface), the surface properties of the uppermost layer are improved, and the adhesion between the upper and lower layers is also improved. As a result, it is possible to meet the required performance of a magnetic tape, for example, which requires high output and low noise for high-density recording, and to perform film peeling even when high durability performance is required. Thus, the film strength is improved and the durability is sufficient. Also, wet on
By the wet multilayer coating method, dropout can be reduced and reliability is improved.

-Smoothing of Surface- In the present invention, the surface is smoothed by calendaring.

After that, burnishing or blade treatment is performed as necessary to perform slitting.

In the surface smoothing treatment, the calendering conditions include temperature, linear pressure, C / s (coating speed).
And the like.

In the present invention, the above temperature is usually set to 50 to
120 ° C, the above linear pressure of 50 to 400 kg / cm, and the above C / s of 20 to 60
It is preferable to keep the pressure at 0 m / min.

The thickness of the uppermost layer resulting from the above treatment is preferably less than 0.5 μm. It is preferable that the layer thickness be 0.5 μm or less, even if the high-frequency characteristics and the overwriting characteristics of signals are improved.

[0117]

Embodiments of the present invention will be described below.

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

A magnetic paint having the following composition was prepared.

[Magnetic paint A for upper layer] 100 parts of Fe-Al based ferromagnetic powder (Fe: Al weight ratio = 100: 8, average major axis length = 0.16 μm, Hc = 1580 Oe, saturation magnetization σs, 120 emu / g, crystallite size = 170 mm, axial ratio = 8) Vinyl chloride resin containing metal sulfonic acid (MR-110, manufactured by Zeon Corporation) 10 parts Polyester polyurethane resin containing metal sulfonic acid salt 3 parts (Toyobo Co., Ltd.) UR-8300, Tg23 ° C) α-alumina (particle size 0.2 μm) 5 parts carbon black (particle size 40 nm) 0.5 part myristic acid 1 part stearic acid 1 part butyl stearate 1 part methyl ethyl ketone 100 parts toluene 100 parts cyclohexanone 100 Part [Magnetic paint B for upper layer] A except that 5 parts of polyester urethane UR-8200 (manufactured by Toyobo Co., Ltd., Tg: 75 ° C) containing metal salt of sulfonic acid was used instead of polyurethane UR-8300 in paint A for upper layer. Similarly magnetic Fee was prepared.

[Lower Layer Coating E] TiO ₂ (average particle size 30 nm) 90 parts Carbon black (average particle size 27 nm) 10 parts Sulfonate metal salt-containing vinyl chloride resin (manufactured by Zeon Corporation, MR-110) 6 Part Polyester polyurethane resin containing sulfonic acid metal salt (Toyobo Co., Ltd., UR-8700, Tg: -20 ° C) 3 parts Alumina (α-Al ₂ O ₃ , average particle size: 0.2 μm) 6 parts Myristic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts [Magnetic paint D for upper layer] Co-substituted barium ferrite (Hc:
1100 Oe, BET 45m ² / g, σ _s ; 64 emu / g, plate ratio; 4) 1
A magnetic paint was prepared in the same manner as in A except that 00 parts was used.

[Lower layer paint I] In the lower layer paint E,
Fe-Al sendust alloy powder instead of TiO ₂ (coercive force Hc = 40A
/ m, Mi = 200H / m, particle size 40 nm), and a coating material was prepared in the same manner as in E.

[Magnetic paint C for upper layer] In paint A for upper layer, 5 parts of polyester polyurethane UR-8700 (Tg: -20 ° C, manufactured by Toyobo Co., Ltd.) was used instead of UR-3800 as the polyurethane instead of UR-3800. A magnetic paint was prepared in the same manner as in A, except that

[Lower layer paint F] In the lower layer paint E,
Polyurethane polyurethane containing metal sulfonate UR-8300 (Toyobo) instead of UR-8700 as polyurethane
A paint was prepared in the same manner as in E except that 3 parts of Tg (manufactured by Co., Ltd.) was used.

[Lower layer paint G] In the lower layer paint E,
A coating material was prepared in the same manner as in E, except that 3 parts of a sulfonic acid metal salt-containing polyester polyurethane (Tg: -50 ° C) was used instead of UR-8700 as the polyurethane.

[Magnetic paint H for upper layer] In the paint A for upper layer, a polyester polyurethane containing a metal sulfonic acid salt (Tg: 110 ° C) 5 instead of UR-8300 as polyurethane was used.
A magnetic coating material was prepared in the same manner as in A except that the parts were used.

Next, 5 parts of a polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the obtained upper layer magnetic paint and lower layer paint, and then a 10 μm thick film was formed by a wet-on-wet method. After coating on the polyethylene terephthalate film of, after performing a magnetic field orientation treatment while the coating film is not dried, and subsequently subjected to drying, performing a surface smoothing treatment with a calendar,
A magnetic layer consisting of a lower layer having a thickness of 2.0 μm and an upper layer having the thickness shown in Table 1 was formed.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene terephthalate film opposite to the magnetic layer, the coating film is dried, and calendered according to the calendering conditions described later. As a result, a 0.8 μm thick back coat layer was formed to obtain a wide original magnetic tape.

[Coating for Back Coat Layer] 40 parts of carbon black (Raven 1035) 10 parts of barium sulfate (average particle size 300 mμ) 25 parts of nitrocellulose 25 parts of polyurethane resin (N-2301 manufactured by Nippon Polyurethane Industry Co., Ltd.) 10 parts of polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) 400 parts of cyclohexanone 250 parts of methyl ethyl ketone 250 parts of toluene The obtained raw material was slit to prepare an 8 mm video tape.

The electromagnetic conversion characteristics, overwrite characteristics and other characteristics of this video tape were measured in the following manner.

<CN Characteristics> A single 9 MHz wave was recorded.
The output level when the signal was reproduced was represented by comparison with a reference sample (Comparative Example 1).

<Overwrite Characteristics> A 2 MHz signal was recorded at a saturation level, and a 9 MHz signal was then recorded (overwritten). The residual output level of the 2 MHz signal was measured. It is assumed that the lower the residual output level, the better the overwrite characteristics.

<Head clog characteristics at low temperature (0 ° C.)>
The tape was run for the entire length in a low-temperature (0 ° C.) environment using S-550 (manufactured by Sony Corporation). <RF output drop at low humidity (40 ° C, 20% RH)> Low humidity (40
(C, 20% RH), the entire length of the tape was run twice using S-550 (manufactured by Sony Corporation), and the decrease in RF output after running was measured.

Table 1 shows the results.

[0135]

[Table 1]

As is clear from Table 1, the examples of the present invention are superior to the comparative examples.

[0137]

The magnetic recording medium of the present invention allows the magnetic layer to be made thinner, has excellent high-frequency electromagnetic conversion characteristics, and has good overwrite characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining simultaneous multilayer coating for manufacturing a magnetic recording medium of the present invention by wet-on-wet coating using an extrusion coating method.

FIG. 2 is a view of a coater head for applying the paint of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support body 10 Extrusion coater 11 Extrusion coater 32 Supply roll 33 Orientation magnet 34 Dryer 37 Super calendar device 38 Calendar roll 39 Take-up roll

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-216812 (JP, A) JP-A-2-105326 (JP, A) JP-A-2-227823 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B 5/70-5/718

Claims (1)

(57) [Claims] 1. A nonmagnetic layer containing a nonmagnetic powder and a polyurethane resin having a glass transition point (Tg) of −40 ° C. to 0 ° C. as a binder, having a thickness of 0.2 μm or more and 0.5 μm or less.
A magnetic recording medium comprising a magnetic layer containing a polyurethane resin having a Tg of less than 0 and a binder having a Tg of 0 ° C to 100 ° C in this order.