JP3395022B2 - 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 digital magnetic recording medium having a smooth magnetic layer surface, excellent electromagnetic conversion characteristics, and a small error rate and dropout.

[0002]

2. Description of the Related Art Conventionally, for the purpose of improving electromagnetic conversion characteristics in a magnetic recording medium, a magnetic recording medium having a multilayer structure in which a layer containing magnetic powder is provided as an upper layer and a layer containing nonmagnetic powder is provided as a lower layer. (For example, JP-A-63-187418 and JP-A-63-191315) have been proposed.

However, these magnetic recording media are
Although the upper layer of the multi-layer structure has a relatively large thickness, the film thickness loss and the self-demagnetization loss become large, and it is difficult to sufficiently obtain the excellent electromagnetic conversion characteristics and running durability required for a digital recording medium. there were.

Further, in JP-A-5-182177, a lower non-magnetic layer in which an inorganic powder is dispersed in a binder is provided on a non-magnetic support, and the non-magnetic layer is provided with a ferromagnetic powder in a wet state. In a magnetic recording medium provided with an upper magnetic layer dispersed in a binder, the upper magnetic layer thickness is 1.0μm or less, and the lower non-magnetic layer is a non-magnetic inorganic powder having a surface layer covered with an inorganic oxide It is described that, by doing so, the dispersibility can be improved, the interface between the lower non-magnetic layer and the upper magnetic layer can be easily controlled, the surface properties of the upper magnetic layer can be secured, and the electromagnetic conversion characteristics can be improved.

Although these techniques have improved the dispersibility of the non-magnetic inorganic particles and have been able to improve the flatness to some extent, their electromagnetic conversion characteristics are not yet satisfactory for digital recording media, and their flatness is particularly high. It was insufficient, and was not satisfactory from the viewpoint of running durability and dropout characteristics.

An object of the present invention is to solve the above problems and prevent surface roughness of the magnetic layer, particularly when forming a plurality of layers on a non-magnetic support, and to have good electromagnetic conversion characteristics and running durability. Another object of the present invention is to provide a magnetic recording medium having a multi-layered structure, which has excellent properties and is suitable as a digital recording medium.

[0007]

An object of the present invention is to provide a magnetic recording medium having a layer containing a certain ferromagnetic metal powder as a magnetic layer, and further having this magnetic layer as the uppermost layer on a non-magnetic support. In order to obtain excellent electromagnetic conversion characteristics and running durability required for a digital recording medium.

[0008]

The above problems can be solved by the following constitution. That is, 1. In a magnetic recording medium having at least one non-magnetic lower layer having a non-magnetic powder dispersed therein and having an uppermost layer having a ferromagnetic metal powder dispersed therein, the ferromagnetic metal powder is a Fe source.
Child, containing Al atoms and atoms of rare earth elements, the non-magnetic powder is a particle formed by depositing Sn and Sb on rutile TiO2 to form a conductive particle surface, the non-magnetic powder having a major axis length of 0. .
It is needle-shaped conductive particles having a particle size of 02 to 0.3 μm and a crystallite size of 5 to 100 nm, and the average abundance ratio of the elements forming the surface of the conductive particles is 50 to 1500 Sn atoms with respect to 100 Ti atoms. S
b A magnetic recording medium having 5 to 200 atoms.

2. The nonmagnetic lower layer obtained by dispersing non-magnetic powder has at least one layer, and a magnetic recording medium having a top layer formed by dispersing a ferromagnetic metal powder, said ferromagnetic metal
The metal powder contains Fe atoms, Al atoms and rare earth element atoms
The non-magnetic powder is a particle formed by depositing Sn and Sb on α-Fe2O3 to form a conductive particle surface, the non-magnetic powder having a major axis length of 0.02 to 0.3 μm and a crystallite size of 5 to 100 nm. The needle-shaped conductive particles, the average abundance of the elements forming the surface of the conductive particles, the Fe atom number 100 to the Sn atom number is 50.
To 1500, and the number of Sb atoms is 5 to 200. A magnetic recording medium.

3. The nonmagnetic lower layer obtained by dispersing non-magnetic powder has at least one layer, and a magnetic recording medium having a top layer formed by dispersing a ferromagnetic metal powder, said ferromagnetic metal
The metal powder contains Fe atoms, Al atoms and rare earth element atoms
However , the non-magnetic powder is a low-order titanium oxide exhibiting conductivity, and the non-magnetic powder has a major axis length of 0.02 to 0.3 μm and a crystallite size of 5.
A magnetic recording medium characterized by being needle-shaped conductive particles of -100 nm.

Low-order titanium oxide (TiO _x : 1 ≤ _X <2) In the magnetic recording medium, the ferromagnetic metal powder in which the magnetic layer is oriented is at least Fe atom and Al as elements forming the surface thereof. Atoms and atoms of rare earth elements are contained, and the average abundance ratio of elements forming the surface of the ferromagnetic powder is 70 to 200 Al atoms with respect to 100 Fe atoms, and 0.5 to 60 atoms of rare earth elements. It is preferable.

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

-Structure of Magnetic Recording Medium- The magnetic recording medium of the present invention comprises a non-magnetic support (A),
A magnetic layer (B) containing a ferromagnetic metal powder is laminated, and the non-magnetic support (A) and the magnetic layer (B) are further laminated.
And a lower layer (C) composed of at least one layer, and in some cases, an appropriate layer is provided above or below the magnetic layer (B).

(A) Non-Magnetic Support The 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 and cellulose die. Examples thereof include cellulose derivatives such as acetate, polyamide, aramid resin, and plastics such as polycarbonate.

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

The thickness of the non-magnetic support is not particularly limited, but, for example, in the case of a film or sheet, it is usually 2
The thickness is 100 μm, preferably 3 to 50 μm. In the case of a disc or a card, it is about 30 μm to 10 mm.

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.

(B) Magnetic Layer The magnetic layer contains magnetic powder. Furthermore, if necessary, a binder and other components can be contained.

The thickness of the magnetic layer is usually 0.02-1.
It is 0 μm, and particularly preferably 0.02 to 0.5 μm. If the thickness is less than 0.02 μm, recording may not be sufficient, and output may not be obtained during reproduction.
On the other hand, if it is larger than 1.0 μm, a sufficient reproduction output may not be obtained as a digital recording medium due to film thickness loss.

(B-1) Magnetic Powder In the present invention, the magnetic layer contains a specific ferromagnetic metal powder described later as an essential magnetic powder.

The ferromagnetic metal powder contains Fe, Al and rare earth element atoms as its constituent elements, and the preferable rare earth element atoms are selected from the group consisting of Sm, Nd, Y, Pr, La and Dy. Is one or more types of atoms.

The ferromagnetic metal powder according to the present invention has a Fe atom content as a weight ratio of elements in the entire ferromagnetic metal powder.
With respect to 100 parts by weight, Al atoms are 2 to 10 parts by weight, atoms of rare earth elements are 1 to 8 parts by weight, and the average abundance ratio of the elements forming the surface of the ferromagnetic metal powder is Fe. It is preferable that the number of Al atoms is 70 to 200 and the number of rare earth elements is 0.5 to 30 with respect to 100 atoms.

More preferably, the ferromagnetic metal powder further contains Na and Ca as constituent elements, and the weight ratio of the elements in the entire ferromagnetic metal powder is such that Na atom is 100 parts by weight with respect to Fe atom. It is less than 0.1 parts by weight and the Ca atom content is 0.1 to
2 parts by weight, Al atoms are 2 to 10 parts by weight, rare earth elements are 1 to 8 parts by weight, and the average abundance of elements forming the surface of the ferromagnetic metal powder is the number of Fe atoms. With respect to 100, the number of Na atoms is 2 to 30, the number of Ca atoms is 5 to 30, the number of Al atoms is 70 to 200, and the number of rare earth element atoms is 0.5 to 30.

More preferably, the ferromagnetic metal powder further contains Co, Ni and Si as its constituent elements, and the weight ratio of the elements in the entire ferromagnetic metal powder is 100 parts by weight of Fe atoms to Co. 2 to 20 parts by weight of atoms and 2 Ni atoms
~ 20 parts by weight, Si atoms 0.3 to 5 parts by weight, Na
Atoms are less than 0.1 parts by weight, Ca atoms are 0.1 to 2 parts by weight, Al atoms are 2 to 10 parts by weight, rare earth element atoms are 1 to 8 parts by weight, and the ferromagnetic metal powder. The average abundance ratio of the elements forming the surface is 100 Fe atoms, less than 0.1 Co atoms, less than 0.1 Ni atoms, 20 to 130 Si atoms, and 20 Na atoms. The number is 2 to 30, the number of Ca atoms is 5 to 30, the number of Al atoms is 70 to 200, and the number of rare earth element atoms is 0.5 to 30.

The ferromagnetic metal powder limited as described above preferably has a high coercive force (Hc) of 1700 Oe or more, more preferably 2000 Oe or more. And
It preferably has a high saturation magnetization (σ _s ) of 120 emu / g or more, and more preferably 140 emu / g or more.

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

In the present invention, the magnetic layer may contain conventionally known magnetic powder.

As the conventionally known magnetic powder, for example,
Compounds represented by FeOx (1.33 <x <1.5), Co-FeOx
Ferromagnetic iron oxide powder such as (1.33 <x <1.5), Fe, Ni, Co
Metal-based metal powders containing as a main component, among these,
Examples include Fe-based metal powders, ferromagnetic metal powders such as Fe-Al-based ferromagnetic metal powders, and hexagonal plate-shaped powders.

The ferromagnetic powder used in the present invention has a major axis diameter of less than 0.30 μm, preferably 0.04 μm.
˜0.20 μm, more preferably 0.05 to 0.17 μm. When the major axis diameter of the ferromagnetic powder is within the above range, the surface property of the magnetic recording medium can be improved and the electromagnetic conversion characteristics can be improved.

In the present invention, the major axis diameter (a) of the ferromagnetic powder contained in the magnetic layer and the major axis diameter (b) of the nonmagnetic powder contained in the lower nonmagnetic layer. The ratio (axial ratio; b / a) is preferably 3 or less, particularly 2.
It is preferably 5 or less, more preferably 2 or less. This is because when the axial ratio is within the above range, excellent properties such as good surface properties of the magnetic recording medium can be exhibited.

The above magnetic powder may be used alone or in combination of two or more kinds.

(B-2) Binder The binder contained in the magnetic layer is typically a vinyl chloride resin such as polyurethane, polyester or vinyl chloride copolymer, and these resins are- It preferably contains a repeating unit having at least one polar group selected from SO ₃ M, —OSO ₃ M, —COOM, —PO (OM ¹ ) ₂ and sulfobetaine group.

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

The above polar group has the 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%. This content is 0.
If it is less than 1 mol%, the dispersibility of the magnetic powder will be reduced, and if the content exceeds 8.0 mol%, the magnetic coating will easily gel. The weight average molecular weight of each resin is 15,0
The range of 00 to 50,000 is preferred.

The content of the binder is 10
0 to 25 parts by weight, preferably 10 to 2 parts by weight
0 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 90:10 to 90% by weight. It is 10:90, preferably 70:30 to 30:70.

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

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-58-108052.
Issue 59-8127, Issue 60-101161, Issue 60-235814, Issue 6
0-238306, 60-238371, 62-121923, 62-146
It is described in the publications such as 432 and 62-146433, and these can also be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described.

Polyesters are 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. Note that other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described.

It is obtained from the reaction of polyols with polyisocyanates.

As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, if a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

Examples of polyisocyanates include diphenylmethane-4,4'-diisocyanate (MDI), hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (ND
I), tolylene diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like.

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

Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₂ M, Cl-C
_{H 2 COOM, Cl-CH 2} -P (= O) (OM 1) 2 As technology relating to the polar groups introduced into the polyurethane, JP-B-58-41565
JP-A-57-92422, 57-92423, 59-8127,
It is described in JP-A-59-5423, JP-A-59-5424 and JP-A-62-121923, 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 50% by weight or less based on the total binder.

The resin has a weight average molecular weight of 10,0.
00-200,000, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose Etc.), styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, and various synthetic rubber resins.

(B-3) Other Components In the present invention, in order to improve the quality of the magnetic layer,
Additives such as an abrasive, a lubricant, a durability improver, a dispersant, an antistatic agent and a conductive fine powder can be contained as other components.

As the polishing agent, a substance known per se can be used.

The average particle size of this abrasive is usually 0.
The thickness is 05 to 0.6 μm, preferably 0.05 to 0.5 μm, and particularly preferably 0.05 to 0.3 μm.

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

Fatty acids and / or fatty acid esters can be used as the lubricant. in this case,
The amount of fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder. If the addition amount is less than 0.2% by weight, the running property is likely to decrease, and if the addition amount is more than 10% by weight, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to decrease.

The amount of the fatty acid ester added is preferably 0.2 to 10% by weight based on the magnetic powder, and particularly preferably
It is 0.5 to 5% by weight. If the added amount is less than 0.2% by weight, the still durability is apt to deteriorate, and if it exceeds 10% by weight, fatty acid ester exudes to the surface of the magnetic layer,
The output is likely to decrease.

When it is desired to enhance the lubricating effect by using a fatty acid and a fatty acid ester together, 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, preferably having 6 to 30 carbon atoms, and 12 to 22 carbon atoms.
Is more preferable.

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

Examples of the curing agent include polyisocyanates. Examples of the polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds,
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 caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and other fatty acids having 12 to 18 carbon atoms; salts of these alkali metals or alkaline earth metals. Salt of
Alternatively, these amides; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having a carboxyl group and / or a sulfonic acid group can be exemplified. These dispersants are usually used in the range of 0.5 to 5% by weight based on the magnetic powder.

Examples of the antistatic agent include cationic surfactants such as quaternary amines; anionic surfactants containing an acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid; aminosulfonic acid and the like. Examples of the amphoteric surfactant include natural surfactants such as saponin. The above-mentioned antistatic agent is usually added in an amount of 0.01 to 40 relative to the binder.
It is added in the range of weight%.

Further, in the present invention, conductive fine powder can be preferably used as the antistatic agent. As the antistatic agent, carbon black, graphite,
Tin oxide film or antimony solid solution tin oxide film with pigment such as tin oxide, silver powder, silver oxide, silver nitrate, organic compound of silver, metal particles such as copper powder, metal oxide such as zinc oxide, barium sulfate and titanium oxide And the like, which are coated with a conductive substance such as.

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

The content of the conductive fine powder is 1 to 20 parts by weight, preferably 2 to 7 parts by weight, based on 100 parts by weight of the magnetic powder.

(C) Lower Layer The lower layer is composed of at least one layer, and is formed, if necessary, with a single layer or a plurality of layers between the non-magnetic support and the magnetic layer.

The lower layer may have other kinds of layers or two or more kinds of layers other than the non-magnetic lower layer shown in the embodiment, and the number is not particularly limited. As the lower layer other than the examples, for example, a magnetic layer containing magnetic powder (C-
1), a non-magnetic layer (C-2) containing a non-magnetic powder, a layer (C-3) containing a high magnetic permeability material, or a layer composed of a combination of these layers. In the present invention, the nonmagnetic layer (C-2) is preferable, and the nonmagnetic layer containing needle-shaped nonmagnetic powder is particularly preferable.

The dry film thickness of the lower layer is usually 0.1 to 2.5 μm.
m, preferably 0.2 to 2.0 μm, particularly preferably 0.5 to 2.0 μm. When the dry film thickness is larger than 2.5 μm, the surface roughness of the upper layer surface after the multi-layering increases, so-called multi-layer surface roughness occurs, and preferable electromagnetic conversion characteristics may not be obtained, while 0.5 μm. If it is smaller than that, it becomes difficult to obtain high smoothness during calendaring, the electromagnetic conversion characteristics are deteriorated, and the meaning of providing the lower layer may be diminished.

(C-1) Nonmagnetic Layer The nonmagnetic layer contains nonmagnetic powder. Further, it contains a binder and other components as necessary.

(C-2-1) Non-Magnetic Powder In the present invention, various known non-magnetic powders can be appropriately selected and used in addition to the non-magnetic powder of the present invention.

Examples of the non-magnetic powder include graphite, TiO ₂ , barium sulfate, ZnS, MgCO ₃ , CaCO ₃ , ZnO and Ca.
O, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-Fe ₂ O ₃ ,
α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, Examples include diatomaceous earth and dolomite.

Of these, CaCO ₃ and Ti are preferable.
O ₂ , barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOO
It is an inorganic powder such as H and Cr ₂ O ₃ . More preferably TiO ₂ , α
—Fe ₂ O ₃ etc.

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

It is preferable to use a non-magnetic powder having a specific surface area within the above range because the surface properties of the non-magnetic layer can be improved and the surface properties of the magnetic layer can be improved.

Further, in the present invention, it is preferable that the non-magnetic powder is surface-treated with a Si compound and / or an Al compound. By using the non-magnetic powder that has been subjected to such surface treatment, the surface condition of the magnetic layer can be improved. The content of Si and / or Al is 0.1 to 10% by weight of Si, Al based on the non-magnetic powder.
Is preferably 0.1 to 10% by weight.

The content of the non-magnetic powder in the non-magnetic layer is usually 50 to 99% by weight, preferably 60 to 95% by weight, based on the total of all components constituting the non-magnetic layer.
And particularly preferably 70 to 95% by weight. When the content of the non-magnetic powder is within the above range, the surface condition of the magnetic layer and the non-magnetic layer can be improved.

(C-2-2) Binder The binder contained in the nonmagnetic layer below the binder is
The compounds exemplified in (B-2) can be used, and the amount thereof is usually 5 to 150 parts by weight, preferably 10 to 120 parts by weight, relative to 100 parts by weight of the non-magnetic powder.

(C-2-3) Other Components As the other components contained in the lower non-magnetic layer, the compounds exemplified in (B-3) can be used. The amount is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected.

The layer containing the high magnetic permeability material may contain non-magnetic particles.

-Manufacture of Magnetic Recording Medium- In the magnetic recording medium of the present invention, in the case of a multi-layer structure, the magnetic layer is coated by a so-called wet-on-wet system in which the lower layer is in a wet state. Is preferred. 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, a magnetic 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 coating, and then the high-concentration magnetic coating is diluted. After preparing the 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) and methyl isobutyl ketone (MI
BK), ketones such as cyclohexanone; alcohols such as methanol, ethanol, propanol; esters such as methyl acetate, ethyl acetate, butyl acetate; cyclic ethers such as tetrahydrofuran; methylene chloride,
Halogenated hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more.

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

Examples of the kneading / dispersing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill,
Kobol Mill, Tron Mill, Sand Mill, Sand Grinder, Sqegvari Attritor, High Speed Impeller Disperser,
High speed stone mill, high speed impact mill, disper, high speed mixer, homogenizer, ultrasonic disperser, open kneader, continuous kneader, pressure kneader and the like can be mentioned. Among the above kneading dispersers, the kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) are a pressure kneader, an open kneader, a continuous kneader, a two roll mill and a three roll mill. is there.

In order to coat the magnetic layer and the lower layer on the non-magnetic support, specifically, as shown in FIG. 1, first, the non-magnetic support 1 fed from the supply roll 32 is applied to the extrusion method. By the extrusion coater 10, 11, 12 of the magnetic coating and the lower layer coating after wet-on-wet multi-layer coating is passed through the orientation magnet, for example, the vertical orientation magnet 33, introduced into the dryer 34, Here, hot air is blown from the nozzles arranged above and below to dry. Next, the dried non-magnetic support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered and then wound on a winding roll 39.
The magnetic film thus obtained can be cut into a tape having a desired width to produce a magnetic recording tape for 8 mm video, for example.

In the above method, each coating material was extruded through an in-line mixer (not shown) and the coaters 10, 1 were used.
It may be supplied to 1 and 12. It should be noted that in the figure, the arrow indicates the conveying direction of the non-magnetic support. Extrusion coater 10, 11, 12
Each of them is provided with liquid reservoirs 13, 14 and 15, and the coating material from each coater is layered in a wet-on-wet system. That is, the magnetic coating material is applied in multiple layers immediately after the application of the lower layer coating material (when it is in an undried state).

The extrusion coater shown in FIG.
In addition to the two extrusion coaters 5a and 5b shown in (a), it is also possible to use the extrusion coaters 5d and 5e of the type shown in FIGS. 2 (b) and 2 (c). The coaters shown in FIGS. 3A, 3B and 3C can be used for the triple layer coating. Further, as the multi-layer coating, the above coaters may be combined and coated. Among these, Figure 2
The extrusion coater 5e shown in (c) is preferred in the present invention. The lower coat material 3 and the magnetic paint 4 are co-extruded by the extrusion coater 5e to apply multiple layers.

The magnetic field in the oriented magnet or the vertical orientation 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 °.
It's about a minute.

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. Further, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater and the like can be combined.

In the multi-layer coating in the wet-on-wet system, since the magnetic layer is coated while the lower layer located under the magnetic layer is in a wet state, the surface of the lower layer (that is, the boundary with the magnetic layer). The surface is smooth and the surface properties of the magnetic layer are good, and the adhesiveness between the upper and lower layers is also improved. As a result, especially for high-density recording, high output and low noise are required, for example, the performance required as a magnetic tape is satisfied, and high durability performance is required. To improve the film strength,
Sufficient durability. Further, the wet-on-wet multi-layer coating method can also reduce dropout and improve reliability.

-Surface smoothing-In the present invention, it is also possible to carry out a surface smoothing process by calendering.

Thereafter, if necessary, burnishing or blade processing is performed for slitting.

In the surface smoothing treatment, temperature, linear pressure, C / S (coating speed) and the like can be mentioned as calendering conditions.

In the present invention, the above temperature is usually 50
~ 140 ° C, the above linear pressure is 50 ~ 400kg / cm, the above C / S is 20
It is preferable to hold at 1,000 m / min. If these values are not satisfied, it may be difficult or impossible to keep the surface properties of the magnetic recording medium in good condition.

The thickness of the magnetic layer obtained as a result of the above treatment is set to 0.02 to 1.0 μm. If the thickness of the layer exceeds 1.0 μm, the electrical characteristics deteriorate, so that a magnetic recording medium suitable as a digital recording medium, which is the object of the present invention, cannot be obtained.

A cross-sectional view of the magnetic recording medium thus obtained is shown in FIG.

[0097]

Embodiments of the present invention will be described below.

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

The respective components of the uppermost layer magnetic coating material and the lower layer coating material having the following compositions were kneaded and dispersed using a kneader and a sand mill to prepare an uppermost layer magnetic coating material and a lower layer coating material.

[0100] {Magnetic paint}   Ferromagnetic metal powder (U-1 to U-15 shown in Table 1) 100 parts   Vinyl chloride resin containing potassium sulfonate group   (Nippon Zeon Co., Ltd. MR-110) 10 parts   Polyurethane resin containing sodium sulfonate group   (Toyobo Co., Ltd., UR-8700) 10 parts   α-alumina (0.15μm) 8 parts   Stearic acid 1 part   Butyl stearate 1 part   Cyclohexanone 100 parts   100 parts of methyl ethyl ketone   100 parts of toluene

[0101]

[Table 1]

{Coating for lower layer} Powder for lower layer (A to U, a to r shown in Tables 2 and 3) 100 parts Vinyl chloride resin containing potassium sulfonate group (MR-110 manufactured by Nippon Zeon Co., Ltd.) 12 parts Sodium sulfonate group-containing polyurethane resin (UR-8700, manufactured by Toyobo Co., Ltd.) 8 parts α-alumina (average particle size: 0.2 μm) 5 parts Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 Parts Toluene 100 parts To each of the obtained magnetic paint and lower layer paint, 5 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added.

[0103]

[Table 2]

[0104]

[Table 3]

Using the above-mentioned magnetic coating material containing a ferromagnetic metal powder shown in Table 1 and the lower layer coating material containing a non-magnetic powder shown in Table 2, a wet-on-wet system was used. After coating on a 10 μm polyethylene terephthalate film, magnetic field orientation treatment is performed while the coating film is undried, followed by drying and then surface smoothing treatment with a calendar, which is shown in Tables 4 and 5. A magnetic layer having a thickness and a lower layer and an uppermost layer was formed.

[0106]

[0107]

[Table 5]

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

Carbon black (Raven 1035) 40 parts Barium sulfate (average particle size 300 nm) 10 parts Nitrocellulose 25 parts Polyurethane resin (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Polyisocyanate compound (Nippon Polyurethane Co., Ltd. ), Coronate L) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts The original antimagnetic tape thus obtained is slit into 8 mm.
A wide width magnetic recording medium for video was prepared. The following evaluations were performed on this magnetic recording medium. The results are shown in Tables 7 and 8.

<< Evaluation >><SurfaceResistivity> Test Method: As shown in FIG. 5, two rod-shaped metal electrodes 40 each having a cross section of a quarter circle with a radius of about 10 mm were used.
A weight of 160 g each is hung on both ends of a magnetic tape 41 placed 12.7 mm apart and in contact with the magnetic surface of the tape at a right angle, and a measurement voltage of DC 500 ± 50 V is measured using an insulation resistance meter. In addition to the electrodes, the resistance value is measured and this is taken as the surface specific resistance. The measurement should be performed after leaving the sample in a relative humidity of 30% for 24 hours.

<Dropout> (D / 0) Dropout counter VD-5M manufactured by Victor Company of Japan
Was used for 15 μsec or more and the output of the Rf envelope was reduced by 20 dB or more as one dropout, and the total length was measured to obtain the average value per minute.
(Measurement Unit: Pieces / Minute) <Surface Roughness R _10z > Measured using a Talystep roughness meter (Rank Taylor Hobson).

As a measurement condition, a stylus is 2.5 × 0.1.
μm, needle pressure 2mg, cut-off filter 0.33H
z, measurement speed was 2.5 μm / sec, and reference length was 0.5 mm.

In the roughness curve, the unevenness of 0.002 μm or less is cut.

<Electrical characteristics (dB) RF output> Sony Corporation
8mm video camera CCDV-900 made, RF at 7MHz
The output was measured.

<Elemental analysis value> Orientation used in the present invention,
The average abundance ratio of elements forming the surface of the ferromagnetic metal powder present in the dried magnetic coating film and the surface of the non-magnetic powder present in the non-magnetic coating film is measured using an XPS surface analyzer. To do.

Next, the XPS surface analyzer for explaining the method is set under the following conditions.

X-ray anode; Mg resolution; 1.5 to 1.7 eV (resolution is defined by the full width at half maximum of 3d5 / 2 peak of normal Ag.) The XPS surface analyzer is not particularly limited, and any model can be used. However, in the present invention, V
ESCALAB-200R manufactured by G company was used.

Narrow scan was performed in the following measurement range,
The spectrum of each element was measured. At this time, the data capturing interval is set to 0.2 eV, and it is necessary to integrate until the target peak has a count not less than the minimum count shown in Table 6.

The energy position of the obtained spectrum is corrected so that the peak position of Cl _s becomes 284.6 eV.

Next, COMMON DATA PRO made by VAMAS-SCA-JAPAN
In order to perform processing on CESSING SYSTEM Ver.2.3 (hereinafter referred to as VAMAS software), the spectrum is transferred to a computer capable of using VAMAS software by using software provided by each device manufacturer. And VA
Data processing is performed after converting the transferred spectrum into VAMAS format using MAS software.

Before starting the quantitative processing, Coun for each element
Calibrate t Scale and perform 5-point smoothing. The peak area intensity (cps * e) within the quantitative range shown in Table 6 centered on the peak position of each element
V). Using the sensitivity coefficients shown below, determine the atomic% of each element. The number of atoms is 100 for Fe atoms for ferromagnetic metal powder, and Sn, Sb for TiO ₂ for non-magnetic powder.
The number of Ti atoms deposited is 100 and the number of atoms deposited on α-Fe ₂ O ₃ is 100 Fe atoms.

—Evaluation Preparation Method— Before the above measurement, the medium (magnetic tape) is pretreated.

The binder resin is removed from the magnetic tape by a plasma low humidity ashing treatment method to expose the magnetic particles. The treatment method is selected such that the binder resin is incinerated but the magnetic particles are not damaged. For example, after the treatment was performed under the following apparatus and treatment conditions, the average abundance ratio of elements forming the surface of the oriented ferromagnetic metal powder was measured.

For the lower non-magnetic powder, the surface of the tape was polished with a polishing tape to expose the non-magnetic lower layer,
The plasma low-humidity ashing treatment was performed to measure the average abundance ratio of the elements forming the surface of the non-magnetic powder.

Device: Reiwa Shoji PL-850X Processing condition: FORWARD POWER 100W REFLECTED POWER 5W Vacuum degree 10Pa Introduced gas type Air Discharge time 1 min

[0126]

[Table 6]

[0127]

[0128]

[Table 8]

It can be seen that the structure of the present invention has excellent surface smoothness and electromagnetic conversion characteristics.

Example 2 Two layers, a lower layer (1) and a lower layer (2) of the lower non-magnetic layer, were prepared.
A triple-layer magnetic recording medium was prepared in the same manner as in Example 1 except that the magnetic layer, the lower layer (1), and the lower layer (2) were coated in this order from the surface side so as to have the film thicknesses shown in Table 9. The same evaluations as in Example 1 were performed, and the results are shown in Table 10.

[0131]

[Table 9]

[0132]

[Table 10]

It can be seen that the structure of the present invention has excellent surface smoothness and electromagnetic conversion characteristics.

[0134]

As described above, excellent surface smoothness can be obtained, and excellent running durability and electromagnetic conversion characteristics can be obtained.

[Brief description of drawings]

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

FIG. 2 is a sectional view of an extrusion coater head.

FIG. 3 is another cross-sectional view of the extrusion coater head.

FIG. 4 is a sectional view of a magnetic recording medium.

FIG. 5 is a diagram showing a method for measuring surface resistivity.

[Explanation of symbols]

1 Non-magnetic support 2 Lower layer (2) paint 3 Lower layer (1) paint 4 magnetic paint 5a, 5b, 5c, 5d, 5e Extrusion coater 10, 11, 12 Extrusion coater 13, 14, 15 Liquid reservoir 32 supply rolls 33 Vertical orientation magnet 34 dryer 37 Super calendar device 38 calendar rolls 39 Take-up roll 40 electrodes 41 magnetic tape

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 5-182177 (JP, A) JP 5-298658 (JP, A) JP 6-52540 (JP, A) JP 5- 290354 (JP, A) JP-A-6-25702 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/62-5/82

Claims (3)

(57) [Claims] 1. A nonmagnetic lower layer obtained by dispersing non-magnetic powder has at least one layer, and a magnetic recording medium having a top layer formed by dispersing a ferromagnetic metal powder, said ferromagnetic metal
The metal powder contains Fe atoms, Al atoms and rare earth element atoms
The nonmagnetic powder is a particle in which Sn and Sb are deposited on rutile TiO ₂ to form a conductive particle surface, and the nonmagnetic powder has a major axis length of 0.02 to 0.3 μm and a crystallite size of 5 to 100 nm. The needle-shaped conductive particles of, the average abundance ratio of the elements forming the surface of the conductive particles, the number of Sn atoms is 5 for 100 Ti atoms.
A magnetic recording medium having 0 to 1500 and Sb atom number of 5 to 200. 2. A having at least one layer of non-magnetic lower layer obtained by dispersing non-magnetic powder, and a magnetic recording medium having a top layer formed by dispersing a ferromagnetic metal powder, said ferromagnetic metal
The powder contains Fe atoms, Al atoms and rare earth element atoms
The nonmagnetic powder is a particle in which α and Fe ₂ O ₃ are coated with Sn and Sb to form a conductive particle surface, and the nonmagnetic powder has a major axis length of 0.02 to 0.3 μm and a crystallite size of 5 ~ 100 nm needle-shaped conductive particles, the average abundance of the elements forming the surface of the conductive particles, the Fe atom number 100 to the Sn atom number is 50
To 1500, and the number of Sb atoms is 5 to 200. A magnetic recording medium. 3. A non-magnetic lower layer obtained by dispersing non-magnetic powder has at least one layer, and a magnetic recording medium having a top layer formed by dispersing a ferromagnetic metal powder, said ferromagnetic metal
The powder contains Fe atoms, Al atoms and rare earth element atoms
However , the non-magnetic powder is a low-order titanium oxide exhibiting conductivity, and the non-magnetic powder has a major axis length of 0.02 to 0.3 μm and a crystallite size of 5.
A magnetic recording medium characterized by being needle-shaped conductive particles of -100 nm. Low-order titanium oxide (TiO _X : 1 ≦ X <2)