JPH0922520A - Magnetic disk and production of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease generation of errors in fast rotation by forming an uppermost layer having a ferromagnetic powder dispersed in a binder on a lower layer having a nonmagnetic powder dispersed in a binder and controlling the thermal volume change rate to a specified value or lower. SOLUTION: A film supporting body 40 released from a supply roll 32 is heat treated for 0.36-1.2sec at 40-80 deg.C as the base standard point in a heat treating furnace 31. Then after coating materials are applied and laminated by wet-on-wet method by extrusion coating machine 41, 42, the coating films are oriented by oriented or non-oriented magnets 33, 35, and dried in a drying device 34. The lower layer is prepared, for example, by dispersing a nonmagnetic powder such as α-Fe2 O3 in a binder. The upper layer is prepared, for example, by dispersing a ferromagnetic metal powder such as γ-Fe2 O3 in a binder. In this constitution, the thermal volume change rate at -20 deg.C to 80 deg.C is suppressed within ±0.1% of the volume at 20 deg.C, production of errors in fast rotation can be decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk and a method for manufacturing a magnetic disk, and more particularly to a magnetic disk and a method for manufacturing a magnetic disk capable of high-capacity recording with few errors even at high speed rotation and good modulation characteristics. It is about.

[0002]

2. Description of the Related Art In recent years, the development of a thin film multilayer coating type medium having a non-magnetic layer as a lower layer has been actively pursued mainly for application to a large capacity recording medium. To increase the recording capacity, it is necessary to improve the recording density. The recording density is improved by making the ferromagnetic powder fine. Further, improvement of recording density is being studied by reducing the track width and increasing the rotation speed of the magnetic disk.

On the other hand, with the spread of minicomputers and personal computers as OA equipment, the frequency of use of magnetic disks has spread,
Regarding temperature and humidity, it has come to be used under a wide range of environmental conditions. Even in such an environment, although the track width was reduced and the disk was rotated at a high speed due to the improvement in the recording density described above, there was a problem that the head was apt to cause track deviation due to thermal contraction of the support. .

As a solution to this problem, improving the mechanical characteristics of the magnetic disk has been considered. Japanese Patent Laid-Open No. 5-29
Japanese Patent No. 0361 discloses an invention for improving the head touch by defining the Young's modulus and the film thickness of a magnetic disk.

In these inventions, since the change in volume of the disk in the circumferential direction is not taken into consideration, track deviation may occur when used in an environment where the temperature changes greatly.

Further, Japanese Patent Laid-Open No. 5-314473 proposes a magnetic disk in which a flexible disk sheet having a recording layer on one surface is attached to a support on both sides of a disk-shaped rigid base. There is a problem that the manufacturing cost such as raw material cost and processing cost is higher than that of the flexible disk.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is not to cause an error even at high speed rotation.
Another object of the present invention is to provide a magnetic disk capable of high-capacity recording with good modulation characteristics and a method for manufacturing the magnetic disk.

[0008]

The above-mentioned objects of the present invention have been achieved by the following constitutions.

(1) At least one lower layer obtained by dispersing a non-magnetic powder in a binder is provided on a non-magnetic support,
In a magnetic disk provided with an uppermost layer having ferromagnetic powder dispersed in a binder, a magnetic disk of -20
A magnetic disk having a rate of change in heat volume in the range of 80 to 80 ° C. within ± 0.1% of the volume of the magnetic disk at 20 ° C.

(2) The magnetic disk according to the above item 1, wherein the ferromagnetic powder is a ferromagnetic metal powder.

(3) At least one lower layer obtained by dispersing a non-magnetic powder in a binder is provided on a non-magnetic support,
A magnetic disk provided with an uppermost layer in which ferromagnetic powder is dispersed in a binder.
In a method for producing a magnetic disk, the rate of change in heat volume at 0 ° C is within ± 0.1% of the volume of the magnetic disk at 20 ° C.
Temperature of 0.36 ~ 1.2sec with respect to the base reference point
A method of manufacturing a magnetic disk, which comprises processing.

(4) The method for producing a magnetic disk as described in the above item 3, wherein the ferromagnetic powder is a ferromagnetic metal powder.

The magnetic disk of the present invention will be described in detail below.

In the magnetic disk of the present invention, a magnetic layer containing a ferromagnetic metal powder and at least one non-magnetic layer are provided between the non-magnetic support and the magnetic layer on the non-magnetic support. It is a thing.

<Non-Magnetic Support> Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetates, and cellulose die. Examples thereof include cellulose derivatives such as acetate, polyimides, polyamides, aramid resins, plastics such as polycarbonates, and the like.

Among these, polyethylene terephthalate, polyethylene-2,6-naphthalate, polyimide, polyamide and aramid resin are excellent in the film strength and heat shrinkage ratio of the disk medium.

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,
For example, in the case of film or sheet, it is usually 3 to 100μ.
m, 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 Young's modulus of these non-magnetic supports is 500 to 2000 Kg / mm ² , especially 600
˜1800 Kg / mm ² is preferable. Young's modulus is 500
If it is smaller than Kg / mm ² , the Young's modulus of the disk medium itself becomes small and the disk tends to shake.
If the Young's modulus exceeds 2000 Kg / mm ² , the head of the disk medium may come into contact with the head too strongly, which may cause peeling of the magnetic layer or head failure.

The thermal contraction rate of these non-magnetic supports is within 0.1% in the temperature range of -20 ° C to 80 ° C with respect to the volume of 20 ° C. If the thermal shrinkage exceeds 0.1%, the magnetic disk rotated at a high speed cannot accurately trace a track when a large environmental temperature change occurs.

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

A back coat layer is 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. It is preferable that an undercoat layer be provided between the magnetic layer and the non-magnetic support.

If desired, an overcoat layer may be provided on the uppermost magnetic layer. When the magnetic recording is in the form of a disk, a magnetic layer and an undercoat layer can be provided on both sides with the support sandwiched.

<Upper magnetic layer> The thickness of the upper magnetic layer is 0.
5 μm or less, preferably 0.01 to 0.5 μm
And less than 0.02 to 0.3 μm. If the dry film thickness of the magnetic layer is less than 0.01 μm, recording may not be performed sufficiently, and thus output may not be obtained during reproduction, while if it is 0.5 μm or more, sufficient reproduction may occur due to film thickness loss. Output may not be obtained. Further, the coercive force Hc of the magnetic recording medium is 1200 to 2500 O
e, preferably 1200 to 2500 Oe, and more preferably 1400 to 2300 Oe. In this range, sufficient recording can be obtained.

<Magnetic Powder> Examples of the magnetic powder used in the present invention include ferromagnetic iron oxide powder, ferromagnetic metal powder, and hexagonal plate powder.

Of these, the ferromagnetic metal powder described below is preferable.

Ferromagnetic metal powders used in the magnetic layer include Fe, Co, Fe-Al system, and 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-
Examples include ferromagnetic metal powders such as Ni—P-based, Ni—Co-based, metal magnetic powders containing Fe, Ni, Co and the like as main components. Among these, the 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-Co-Al-C
Fe-Al type ferromagnetic metal powders such as a type are preferable.

Particularly preferred ferromagnetic metal powders for the purpose of the present invention are metal magnetic powders containing iron as a main component.
1 or Al and Ca, in the weight ratio of Al: Fe: Al = 100: 0.5 to 100: 20, and in the case of Ca, the weight ratio of Fe: Ca = 100: 0.1 to 100:
It is desirable to contain it in the range of 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.

Although the reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, it is considered that the coercive force is improved and the aggregates are decreased due to the improved dispersibility.

In addition to the ferromagnetic metal powders described above, Fe, Al, and one or more rare earth elements selected from the group consisting of Sm, Nd, Y, and Pr as the constituent elements are also specified. It is also possible to use ferromagnetic metal powders.

As such a specific ferromagnetic metal powder, the abundance ratios of Fe, Al, and one or more rare earth elements selected from the group consisting of Sm, Nd, Y, and Pr in the overall composition are as follows: Al atom is 2 to 10 parts by weight with respect to 100 parts by weight of Fe atom, and Sm, Nd and Y
1 to 8 parts by weight of one or more rare earth elements selected from the group consisting of
e, Al, and the presence ratio of one or more rare earth elements selected from the group consisting of Sm, Nd, Y, and Pr are F
e The number of Al atoms is 70 to 200 with respect to 100, and the number of one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr is 0.5 to 30. Is preferred.

More preferably, the specific ferromagnetic metal powder further contains Na and Ca as constituent elements, and Fe, Al, Sm, Nd and Y in the entire composition thereof.
The abundance ratio of one or more rare earth elements selected from the group consisting of and Pr, Na and Ca is 2 to 10 parts by weight with respect to 100 parts by weight of Fe atoms, and Sm, Nd, and Y. One or more rare earth elements selected from the group consisting of Pr and 1 to 8 parts by weight, Na atoms are less than 0.1 parts by weight, Ca atoms are 0.1 to 2 parts by weight,
In addition, the abundance ratio of one or more rare earth elements selected from the group consisting of Fe, Al, Sm, Nd, Y, and Pr, Na and Ca on the surface thereof is 100 for Fe atoms, and the number of Al atoms is 70 to 200, Sm and Nd
The number of one or more rare earth elements selected from the group consisting of Y, Pr and Y is 0.5 to 30, and the number of Na atoms is 2
The number of Ca atoms is 5 to 30.

More preferably, the specific ferromagnetic metal powder further contains Co, Ni and Si as its constituent elements, and Fe, Co, Ni, A in the overall composition thereof.
The proportion of one or more rare earth elements selected from the group consisting of 1, Si, Sm, Nd, Y and Pr, and Na and Ca is such that the Co atom content is 2 to 100 weight parts of Fe atom.
20 parts by weight, Ni atom is 2 to 20 parts by weight,
Al atom is 2 to 10 parts by weight, Si atom is 0.3 to
5 parts by weight, 1 to 8 parts by weight of atoms of one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr, Na atoms less than 0.1 parts by weight, Ca Atoms are 0.1 to 2 parts by weight, and Fe, Co, Ni, Al, Si, Sm, Nd, Y and Pr on the surface thereof.
One or more rare earth elements selected from the group consisting of
With respect to the abundance ratio of a and Ca, the number of Co atoms is less than 0.1 and the number of Ni atoms is 0.
Less than 1, the number of Al atoms is 70 to 200, and Si
The number of atoms is 20 to 130, the number of one or more rare earth elements selected from the group consisting of Sm, Nd, Y and Pr is 0.5 to 30, and the number of Na atoms is 2 to 30. , Ca atom number is 5 to 30.

Fe, Co, Ni, and
The abundance ratios of one or more rare earth elements, Na and Ca, selected from the group consisting of Al, Si, Sm, Nd, Y and Pr, are also Fe, Co, Ni, A on the surface.
Ferromagnetic metal powder having an abundance ratio of one or more rare earth elements selected from the group consisting of 1, Si, Sm, Nd, Y and Pr, and Na and Ca within the above range is 1700.
It is preferable because it has a high coercive force (Hc) of Oe or higher, a high saturation magnetization amount (σ _s ) of 120 emu / g or higher, and high dispersibility.

The content of the specific ferromagnetic metal powder is usually 60 to 95 based on the total solid content in the layer.
%, Preferably 70 to 90% by weight, particularly preferably 75 to 85% by weight.

Regardless of which type of ferromagnetic metal powder is used, in the present invention, the magnetic layer contains ferromagnetic iron oxide powder, hexagonal plate-like powder or the like instead of the ferromagnetic metal powder. May be.

As the ferromagnetic iron oxide powder, γ-Fe is used.
FeO _{x with 2} O ₃ , Fe ₃ O ₄ , or intermediate iron oxides thereof.
A compound represented by (1.33 <x <1.5) or Co
(Cobalt modified) Co-FeO
Examples thereof include compounds represented by _x (1.33 <x <1.5).

Examples of the hexagonal plate-like powder include hexagonal ferrite. Such a hexagonal ferrite is made of barium ferrite, strontium ferrite, or the like, and a part of iron element may be replaced with another element such as Ti, Co, Zn, In, Mn, or Hb. IE for this hexagonal ferrite
EE trans on MAG-18 16 (198)
Since it is described in detail in 2), its content is made a part of the description of this specification.

The ferromagnetic powder used in the present invention is preferably needle-shaped and has a major axis diameter of less than 0.30 μm, preferably 0.04 to 0.20 μm, more preferably 0. It is preferably from 05 to 0.17 μm. When the major axis diameter of the ferromagnetic powder is within the above range, the surface properties of the magnetic recording medium can be improved and the electrical characteristics can be improved. The axial ratio (average major axis length / average minor axis length) is preferably 2 to 20, and more preferably 4 to.
Fifteen.

The ferromagnetic powder preferably has a saturation magnetization amount (σ _s ) which is a magnetic property, usually 70 emu / g or more. If the saturation magnetization amount is less than 70 emu / g, the electromagnetic conversion characteristics may deteriorate. Also,
In particular, when the ferromagnetic powder is a ferromagnetic metal powder, the saturation magnetization amount 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 can be preferably used according to the higher recording density.

This specific surface area and its measuring method are described in "Measurement of powder" (JM Dallavelle,
Clyeorr Jr. Co-authored by Muta and others; published by Sangyo Tosho Co., Ltd.)
170-1171 (Chemical Society of Japan); Maruzen Showa 41
(Published April 30, 2013).

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.

-Lower Layer- In the present invention, the lower layer mainly contains non-magnetic powder, or non-magnetic powder and various known magnetic powders can be appropriately selected and used.

Examples of the non-magnetic powder include carbon black, graphite, TiO ₂ , barium sulfate and Zn.
S, MgCO ₃ , CaCO ₃ , ZnO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO,
SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-F
e ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, diatom Examples thereof include soil and dolomite.

Of these, preferred are carbon black, CaCO ₃ , TiO ₂ , barium sulfate and α-Al _2.
Inorganic powders such as O ₃ , α-Fe ₂ O ₃ , α-FeOOH, and Cr ₂ O ₃ , of which α-Fe ₂ O ₃ and α-FeOO
H is preferred, and α-Fe ₂ O ₃ is particularly preferred.

In the present invention, a non-magnetic powder having a needle-like powder shape can be preferably used. When the acicular non-magnetic powder is used, the smoothness of the surface of the non-magnetic layer can be improved, and the smoothness of the surface of the uppermost layer composed of the magnetic layer laminated thereon can also be improved. Is preferred.

The thickness of the lower layer is usually 0.3 to 2.5.
μm, and preferably 0.5 to 2.0 μm. When the thickness is less than 2.5 μm, the so-called multi-layer surface roughness, which increases the surface roughness of the upper layer surface after the multi-layering, is less likely to occur, and preferable electromagnetic conversion characteristics can be obtained. On the other hand, 0.3 μm
When it is larger, a high smoothness can be obtained at the time of calendaring, and the electromagnetic conversion characteristics are improved.

The shape and axial ratio of the non-magnetic powder can be controlled by combining known methods such as selection of starting materials as starting materials, selection of oxidation-reduction conditions, and selection of sintering inhibitors. You can

The major axis diameter of the acicular nonmagnetic powder used in the lower layer of the present invention or the average particle diameter of nonacicular nonmagnetic powder is 2
0 nm or more and 250 nm or less, preferably 220 n
m or less, and particularly preferably 200 nm or less.

The minor axis diameter of the acicular non-magnetic powder and magnetic powder is usually 10 nm or more and 100 nm or less,
It is preferably 80 nm or less, and particularly preferably 60
nm or less.

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

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

When the non-magnetic powder or the 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 non-magnetic layer or the magnetic layer can be improved, and This is preferable in that the surface property of the uppermost layer, which is the magnetic layer, can be in a good state.

In the present invention, the non-magnetic powder or magnetic powder is preferably surface-treated with a Si compound and / or an Al compound. When the non-magnetic powder subjected to such surface treatment is used, the surface condition of the uppermost layer which is the magnetic layer can be improved. The content of Si and / or Al is 0.1 to 10% by weight of Si and 0.1 to 10% by weight of Al with respect to the non-magnetic powder or the magnetic powder.
It is preferably 10% by weight, more preferably Si
Is 0.1 to 5% by weight, Al is 0.1 to 5% by weight,
Particularly preferably, Si is 0.1 to 2% by weight and Al is 0.1.
1 to 2% by weight is preferable, and in the case of magnetic powder, S
The weight ratio of i and Al is preferably Si / Al ≧ 3. The surface treatment can be carried out by the method described in JP-A-2-83219.

The content of the nonmagnetic powder or the magnetic powder in the lower layer is usually 50 to 99% by weight, preferably 60 to 95% by weight, based on the total of all components constituting the lower layer.
%, Particularly preferably 70 to 95% by weight. When the content of the non-magnetic powder or the magnetic powder is within the above range,
The state of the surface of the uppermost layer composed of the non-magnetic layer and the magnetic layer can be improved.

-Carbon black-The carbon black contained in the magnetic layer is preferably a carbon black having a DBP oil absorption of 110 ml / 100 g to 500 ml / 100 g. For example, Asahi Carbon Black Asahi # 80 (23 nm, 113 ml / 100 g), Columbia Carbon. CONDUCTICS SC (17n
m, 115 ml / 100 g), Conductix 97
5 (20 nm, 183 ml / 100 g), Cabot Monarch 1300 (13 nm, 121 ml / 100)
g), Vulcan XC-72 (30 nm, 178 ml / 1
00g), Vulcan P (20nm, 116ml / 100
g), Vulcan 9 (19 nm, 114 ml / 100)
g), Black Pearls 2000 (15 nm, 330 m
1/100 g) and the like. The carbon black contained in the non-magnetic layer is DB
Carbon black having a P oil absorption of 20 ml / 100 g to 110 ml / 100 g is preferable, for example Raven 500 (12 nm, 95 ml / 100 manufactured by Columbia Carbon Co., Ltd.).
g), Raven 1255 (23 nm, 58 ml / 10
0g), Raven 1035 (27nm, 60ml / 1
00g), Raven2000 (18 nm, 70 ml /
100g), Cabot Black Pearl 1400 (1
3nm, 80ml / 100g), Black Pearl 130
0 (13 nm, 91 ml / 100 g), Black Pearl 1100 (14 nm, 50 ml / 100 g), Black Pearl 900 (15 nm, 64 ml / 100 g), Black Pearl L (24 nm, 55 ml / 100 g), Regal 400 (25 nm, 70 ml / 100 g). ) Etc. The carbon black A contained in the magnetic layer has a number average particle diameter of preferably 10 to 40 nm, more preferably 10 to 30 nm for the purpose of smoothing the surface of the magnetic layer and obtaining high output.

In addition to carbon black A having a number average particle size of 10 to 30 nm in the magnetic layer, a number average particle size of 40 to 500 is further added.
It is particularly preferable that the carbon black B of nm is contained because the running durability in an environment from high temperature to low temperature is improved.

In the carbon black C contained in the non-magnetic layer, the surface property of the upper magnetic layer greatly depends on the thickness of the upper magnetic layer. Therefore, the characteristics of the carbon black C contained in the lower non-magnetic layer are important, the number average particle size is 10 to 40 nm, and the oil absorption is 20 m1 / 100 g to 100 ml / 100 in DBP value.
It is preferable to select carbon black of g in order to improve the dispersibility of the nonmagnetic layer and obtain good surface properties.

The number average particle diameter of carbon black C is preferably 10 to 40 nm, more preferably 10 to 30 nm. Further, the oil absorption or DBP value of carbon black A is preferably 30 to 90 ml / 100 g, and more preferably 40 to 80 ml / 100 g.

The weight of carbon black A contained in the magnetic layer is preferably 0.1 to 5.0% by weight, and more preferably 0.2 to 2.0% by weight, based on the magnetic powder. The weight of the carbon black C contained in the nonmagnetic layer is preferably 5.0 to 30% by weight, more preferably 7.0 to 20% by weight, based on the nonmagnetic powder.

The oil absorption of carbon black (A, B) is D
The BP value is preferably 130 to 350 ml / 100 g, and more preferably 150 to 250 ml / 100 g.

The method of adding carbon black can be variously changed. For example, fine particles of carbon black and coarse particles may be charged into a disperser at the same time and mixed, or only a part of them may be added first, and the remaining amount may be added when the dispersion is advanced to some extent. Good. When importance is placed on the dispersion of carbon black, it is also possible to knead carbon black together with a magnetic material or filler and a binder by a three-roll mill, Banbury mixer or the like, and then disperse with a disperser to obtain a coating material. When importance is attached to conductivity like layers other than the magnetic layer, the carbon black structure structure is less likely to be broken by adding carbon black in the latter half of the dispersion step and the liquid preparation step as much as possible.

A so-called "carbon masterbatch" in which carbon black is kneaded in advance with a binder.
May be used.

Here, the particle size of the above carbon black is directly measured visually by an electron microscope. That is, a magnetic recording medium, for example, a tape is cut in the longitudinal direction to a thickness of about 700Å, and the obtained cross section is observed with a transmission electron microscope (applied voltage 200 KV, magnification 60,000). In this case, the diameter of each particle of carbon black is measured and N = 10
The number average particle size of 0 pieces is defined as "average particle size".

Regarding the above-mentioned "oil absorption (DBP method)", 100 g of pigment powder is used for DBP (Dibutylp).
hthalate) little by little, and observing the state of the pigment while kneading, and when finding a point that forms one lump from the dispersed state, the ml number of DBP is DBP.
The amount of oil absorption.

-Binder- As the binder used in the present invention, for example, vinyl chloride type resins such as polyurethane, polyester, vinyl chloride type copolymer and the like are typical, and these resins are -S.
_{O 3 M, -OSO 3 M,} -COOM, -OPO (OM 1)
And -PO (OM ¹⁾ preferably contains a repeating unit having at least one polar group selected from _2.

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

The polar group has a function of improving the dispersibility of the magnetic 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 10 to 40 parts by weight based on 100 parts by weight of the ferromagnetic powder,
It is preferably 10 to 30 parts by weight.

The binder is not limited to one kind alone, and two or more kinds may 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. It is 10:90, and preferably in the range of 70:30 to 30:70.

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

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 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-based copolymer, JP-A-57-44227 and JP-A-5-44227 have been used.
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 polyester is generally obtained by reacting a polyol with a polybasic acid.

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

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

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

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

Next, for polyurethane, it is obtained from the reaction of a polyol and 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 having a polar group can be synthesized.

In the present invention, it is preferable to use an aromatic polyester polyurethane prepared by using a polyester polyol having an aromatic ring in order to achieve the object of the present invention.

Examples of polyisocyanates include diphenylmethane-4,4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like can be mentioned.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective.

As a technique for introducing a polar group into polyurethane, Japanese Patent Publication No. 58-41565 and Japanese Patent Laid-Open No.
7-92422, 57-92423, 59-8
No. 127, No. 59-5423, No. 59-5424,
It is described in Japanese Patent Publication No. 62-121923 and the like, 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 weight 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 quality of the magnetic layer, additives such as durability improvers, dispersants, abrasives and lubricants may be contained as other components. .

Examples of the durability improver include polyisocyanate, and examples of the polyisocyanate include:
For example, an aromatic polyisocyanate such as an adduct of tolylene diisocyanate (abbreviation: TDI) with an active hydrogen compound, and hexamethylene diisocyanate (abbreviation: H)
There are aliphatic polyisocyanates such as adducts of MDI) with active hydrogen compounds. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3000.

As the dispersant, 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 their amides; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having carboxyl groups and sulfonic acid groups, etc. Can be mentioned. These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the amount of fatty acid added is 0.2 to 10% by weight with respect to the ferromagnetic powder.
Is preferred, and 0.5 to 5% by weight is more preferred. If the addition amount is less than 0.2% by weight, the running property tends to be lowered, and if the addition amount is more than 10% by weight, the fatty acid is likely to seep out to the surface of the magnetic layer or the output is likely to be lowered. 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 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 using a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid and preferably has 6 to 30 carbon atoms.
The range of -22 is more preferable. Specific examples of 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, succinic acid, maleic acid. Acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like can be mentioned.

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 can be mentioned.

As the lubricant other than the above-mentioned fatty acids and fatty acid esters, substances known per se can be used. For example, silicone oil, fluorinated carbon, fatty acid amide, α-olefin oxide and the like can be used.

Next, 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 abrasive has an average particle size of 0.05 to 0.6.
The thickness is preferably μm, more preferably 0.1 to 0.3 μm.

In the present invention, an antistatic agent can be used as a supplement. That is, in addition to the conductive powder such as carbon black and graphite, a cationic surfactant such as quaternary amine; sulfonic acid, sulfuric acid, phosphoric acid,
Examples thereof include anionic surfactants containing an acid group such as phosphoric acid ester and carboxylic acid; amphoteric surfactants such as aminosulfonic acid; and natural surfactants such as saponin. The above-mentioned antistatic agent is usually added to the binder at 0.0
It is added in the range of 1 to 40% by weight.

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

For example, generally, magnetic powder, binder,
A high-concentration paint is prepared by kneading a dispersant, a lubricant, an abrasive, an antistatic agent, etc. and a solvent, and then the high-concentration paint is diluted to prepare a coating paint, and then this paint is non-magnetically supported. Apply to the surface of the body.

Examples of the above-mentioned solvent or solvent for dilution include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; methyl acetate, ethyl acetate, butyl acetate and lactic acid. Esters such as ethyl and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform , Halogenated hydrocarbons 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 disperser include those described in paragraph No. 0112 of JP-A-4-214218. Of the above kneading dispersers, 0.
The kneading disperser capable of providing a power consumption load of 05 to 0.5 KW (per 1 kg of magnetic powder) includes a pressure kneader, an open kneader, a continuous kneader, a two-roll mill and a three-roll mill.

To apply the constituent layers onto the non-magnetic support, specifically, as shown in FIG.
The heat treatment furnace 3
In 1, the support is heat-treated at a temperature of 40 to 80 ° C. for 0.36 to 1.2 sec with respect to the base reference point. Here, the base reference point is a point for taking a time from when the point enters the heat treatment furnace 31 to when the point exits with the point having the base as a reference.

Next, each coating material is wet-on by the extrusion type extrusion coaters 41 and 42.
After multi-layer coating by a wet method, after orientation treatment with oriented or non-oriented magnets 33 and 35, a drying device 34
Dry by. Here, the orienting or non-orienting magnet may be installed in the drying device or may be installed in front of the drying device.

The wet film thickness as used herein means the total film thickness immediately after wet-on-wet coating of the lower layer coating material containing the non-magnetic powder and the magnetic coating material for the magnetic layer.

Next, the dried support 40 with each coating layer is formed.
Is guided to a super calendar device 37 composed of a combination of calender rolls 38, subjected to calendering here, and then wound on a winding roll 39. The magnetic film thus obtained is cut into a disk of a desired size, for example,
3.5 inch floppy disks can be manufactured.

In the above method, each paint may be supplied to the extrusion coaters 41 and 42 through an in-line mixer (not shown). In the figure, arrow D indicates the transport direction of the non-magnetic support film. Extrusion coaters 41 and 42 are provided with liquid pool portions 43 and 44, respectively, and the coating materials from the coaters are superposed on each other in a wet-on-wet system. That is, immediately after the coating of the lower layer constituent layer coating material (when it is in a non-dried state), the uppermost magnetic layer coating material is finally applied in multiple layers.

As the coater head, there are heads such as those shown in FIGS. 2A, 2B and 2C.
Heads are preferred in the present invention. When applying three or more layers by the wet-on-wet method, a method such as using three or more extrusion coaters or an extrusion coater having three or more slits is used. The magnetic coating material for the upper layer is extruded to apply multiple layers.

The magnetic field in the oriented magnet or non-oriented magnet is about 20 to 10,000 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.

In the wet-on-wet system, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, etc. can also be used. Furthermore, air doctor coater, blade coater,
Air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater,
A spray coater or the like can be combined.

In the multi-layer coating in this wet-on-wet system, since the upper magnetic layer is coated while the lower layer located below the upper layer is in a wet state, the surface of the lower layer (that is, the boundary with the uppermost layer). The surface becomes smooth and the surface property of the uppermost layer becomes good, and the adhesiveness between the upper and lower layers is also improved. As a result, the high performance, low noise required for high density recording, the performance required as a magnetic disk is satisfied, and the high durability performance is required. , The film strength is improved, and the durability is sufficient. In addition, the wet-on-wet multi-layer coating method can reduce dropout and improve reliability.

-Surface smoothing-In the present invention, surface smoothing may be performed next by calendering. After that, a burnishing treatment or a blade treatment is performed as necessary to perform slitting.

In the surface smoothing treatment, the calender conditions are temperature, linear pressure, and c / s (coating speed).
And the like.

In the present invention, the above temperature is usually set to 50.
It is preferable to maintain the temperature at ˜140 ° C., the linear pressure at 50 to 400 kg / cm, and the c / s at 20 to 1000 m / min.

[0120]

EXAMPLES The present invention will be specifically described below with reference to examples, but the components, ratios, and operation sequences shown below can be variously changed without departing from the scope of the present invention. In addition,
In the following examples, all "parts" are parts by weight.

Example 1 A magnetic layer coating material and a lower layer coating material having the following composition formulations were prepared.
Each was kneaded and dispersed using a kneader and a sand mill, and after adding 5 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) to each of the obtained coatings, a thickness of 75 μm was obtained by a wet on wet method.
Samples of Examples 1 to 18 and Comparative Examples 1 to 14 were applied on the films shown in Tables 1 and 2 in the combinations shown in Tables 1 and 2, and subjected to orientation treatment and non-orientation treatment, and then dried. After that, the surface was smoothed with a calendar to prepare a film having the film thickness shown in Table 1. The magnetic film thus obtained was punched into a disk shape having a diameter of 86 mm and housed in a cassette to obtain a 3.5 inch floppy disk.

Table 2 shows the conditions under which the support was heat-treated before coating.

Paint formulation for magnetic layer (Paint A) Fe-Al magnetic metal powder 100 parts Fe: Co: Al: Y = 100: 10: 8: 5 (weight ratio) (average major axis length: 100 nm Axial ratio: 6 Hc: 1800 σs: 135 emu / g Crystallite size: 150 Å) Sulfonic acid metal salt-containing vinyl chloride resin 10 parts (Nippon Zeon Co., Ltd., MR-110) Sulfonic acid metal salt-containing aromatic polyester polyurethane resin 5 parts (Toyobo Co., Ltd. UR-8300) Alumina (α-Al ₂ O ₃ , number average particle size: 0.2 μm) 6 parts Carbon black 0.8 part (average particle size: 40 nm, DBP oil absorption: 150 ml / 100 g) ) Stearic acid 1 part Myristic acid 1 part Butyl stearate 2 parts Oleyl oleate 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Torr Down 100 parts in (paint B) paint A, Fe as Fe-Al-based ferromagnetic metal powder: Co: Al: Ni: Si: Nd = 10
A except that 0: 10: 8: 5: 3: 5 (weight ratio) was used
Same as.

Lower layer coating material (coating a) 100 parts of α-Fe ₂ O ₃ (average major axis length: 150 nm, 0.2% by weight of Si relative to α-Fe ₂ O ₃ , Al in α-Fe ₂ 1.0% by weight relative to O ₃ , acicular ratio 8, BET: 50 m ² / g) Carbon black (number average particle size: 15 nm) 15 parts Vinyl chloride resin containing sulfonic acid metal salt 6 parts (Japan Zeon Co., Ltd., MR-110) Sulfonic acid metal salt-containing aromatic polyester polyurethane resin 3 parts (Toyobo Co., Ltd. UR-8300) Alumina (α-Al ₂ O ₃ , number average particle size: 0.3 μm) 6 parts Myristic acid 1 part Butyl stearate 2 parts Oleyl oleate 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts (Paint b) Titanium oxide 1 instead of α-Fe ₂ O ₃ in paint a 00 parts (average particle size 30 nm, 0.2% by weight of Si with respect to TiO _2, 1.0% content by weight relative to the TiO ₂ Al) addition to the same paint a.

The characteristics of this floppy disk were measured according to the following items.

(1) Number of Defects A rectangular wave signal of 2.5 MHz was recorded on the disk rotated at 2000 rpm. The number of defects in all the tracks was examined by using the peak value of the reproduced signal of 45% or less of 1/2 of the average signal amplitude of the reproduced signal of one track as a missing pulse.

(2) Modulation A sine wave signal of 25 signals (500 KHz) was recorded by using the following drive, the reproduction output was measured, and from the maximum value A and the minimum value B in one revolution of the reproduction waveform, (A-B ) / (A + B) × 100 (%) was determined. The smaller the difference between A and B, the better.

Drive: Toshiba 4MB drive PD
-211 Measurement track: 79 tracks (3) Heat of base Heat the volume of the base measured in advance for 30 minutes at a temperature of 100 ° C, measure the volume of the base, and calculate the shrinkage amount.

(4) Thermal Volume Change Rate Each magnetic disk whose volume was measured in advance was -20
After being put in the temperature of 0 ° C, 0 ° C, 20 ° C, 40 ° C, 60 ° C, and 80 ° C for 30 minutes, the volume of the magnetic disk was measured and the shrinkage amount was calculated. The rate of change in the heat volume of the disk was used.

[0130]

[Table 1]

[0131]

[Table 2]

As shown in the table, according to the constitution of the present invention,
It can be seen that the reproduction output is high and the modulation characteristics are excellent.

[0133]

According to the structure of the present invention, it is possible to provide a magnetic disk which does not cause an error even at high speed rotation and which enables high-capacity recording with good modulation characteristics, and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is a diagram showing wet-on-wet simultaneous multilayer coating of a magnetic layer by an extrusion coating method.

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

[Explanation of symbols]

 31 heat treatment furnace 32 supply rolls 33, 35 magnets for orientation or non-orientation 34 dryer 37 super calender device 38 calendar roll 39 winding roll 40 support 41 coater 42 coater

Claims (4)

[Claims] 1. A non-magnetic support is provided with at least one lower layer in which a non-magnetic powder is dispersed in a binder, and an uppermost layer is obtained in which a ferromagnetic powder is dispersed in the binder. For magnetic disks, the magnetic disk temperature is -20 ° C to 8 ° C.
A magnetic disk having a thermal volume change rate at 0 ° C. within ± 0.1% of the volume of the magnetic disk at 20 ° C. 2. The magnetic disk according to claim 1, wherein the ferromagnetic powder is a ferromagnetic metal powder. 3. A nonmagnetic support is provided with at least one lower layer in which a nonmagnetic powder is dispersed in a binder, and an uppermost layer in which a ferromagnetic powder is dispersed in the binder is provided thereon. Magnetic disk, the magnetic disk -20 ℃ ~ 80 ℃
In the method for manufacturing a magnetic disk in which the rate of change in heat volume is within ± 0.1% of the volume of the magnetic disk at 20 ° C., a temperature of 40 to 80 ° C. is used as a base reference point for the non-magnetic support immediately before coating. The method for manufacturing a magnetic disk is characterized by performing 0.36 to 1.2 seconds. 4. The method of manufacturing a magnetic disk according to claim 3, wherein the ferromagnetic powder is a ferromagnetic metal powder.