JPH10261220A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is formed with a magnetic layer having a good surface characteristic in the case of the recording medium provided with a nonmagnetic layer as a lower layer and the magnetic layer on the lower layer, has excellent electromagnetic conversion characteristics, has the good shape of an RF envelope, is further suppressed in drop-out and has excellent traveling durability and a process for producing the same. SOLUTION: This medium has the nonmagnetic layer 2 as the lower layer and the magnetic layer 3 on the lower layer. In such a case, a silicone-base leveling agent is incorporated into at least the magnetic layer 3 at 0.05 to 1 pt.wt. and at a specific ratio (the ratio when the coating material for forming the magnetic layer 3 is assumed to be 100 pts.wt.). In such a case, the silicone- base leveling agent is incorporated into at least the magnetic coating material of the nonmagnetic coating material and the magnetic coating material at >=0.05 to <=1 pt.wt. and at a specific ratio per 100 pts.wt. magnetic coating material. The magnetic coating material is applied to a nonmagnetic base 11 by wet-on-wet coating, by which the nonmagnetic layer 2 and the magnetic layer 3 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording medium comprising, as a lower layer, a nonmagnetic layer composed of a nonmagnetic powder and a binder, and a magnetic layer composed of a magnetic powder and a binder provided on the lower layer. Magnetic tape, magnetic disk, etc.) and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a video tape, an audio tape, a magnetic disk or the like, a ferromagnetic powder such as a ferromagnetic iron oxide, a Co-modified iron oxide, CrO ₂ , and a ferromagnetic alloy powder is dispersed in a binder. Having a magnetic layer formed by applying the prepared magnetic paint on a non-magnetic support,
So-called coating type magnetic recording media are widely used.

[0003] In recent years, in the field of magnetic recording, higher recording density and shorter recording wavelength have been promoted. It has been required to have characteristics corresponding to the shortening of the wavelength.

Here, in a coating type magnetic recording medium,
As a technique for improving the electromagnetic conversion characteristics in a high-density recording area, a method of reducing the thickness of a magnetic layer is exemplified. When the magnetic layer is made thinner, self-demagnetization loss at the time of recording and thickness loss at the time of reproduction are reduced, and the electromagnetic conversion characteristics are effectively improved.

However, in this case, when the thickness of the magnetic layer is reduced to, for example, 2 μm or less, the surface shape of the non-magnetic support is easily raised on the surface of the magnetic layer, and the surface of the magnetic layer becomes rough. As a result, the electromagnetic conversion characteristics may be deteriorated due to spacing loss, and dropout may frequently occur.

Therefore, in a coating type magnetic recording medium, a relatively thick non-magnetic layer is interposed between the magnetic layer and the non-magnetic support as a lower layer of the magnetic layer. There has been proposed a so-called multilayer coating type magnetic recording medium in which the surface shape hardly appears on the surface of the magnetic layer. In this multilayer coating type magnetic recording medium, a thin magnetic layer (especially 0.3 μm or less) can be formed on a smooth surface, so that excellent electromagnetic conversion characteristics can be obtained in a short wavelength region.

By the way, such a multilayer coating type magnetic recording medium has been coated with a non-magnetic paint on a non-magnetic support, dried and then subjected to a calender treatment as required, and the drying is performed. It is known that the non-magnetic layer is used as a lower layer and a magnetic paint is applied on the lower layer, that is, a so-called wet-on-dry coating method is used.

However, in this coating method, a non-magnetic layer (hereinafter, sometimes referred to as a lower non-magnetic layer) and a magnetic layer (hereinafter, sometimes referred to as an upper magnetic layer) are provided on separate lines. As a result, the manufacturing process is complicated, and the thickness of the upper magnetic layer is limited for the following reasons.

For example, in order to form the upper magnetic layer thinly,
A method of reducing the applied amount of the upper layer paint (magnetic paint) itself, a method of adding a large amount of a solvent to the magnetic paint to dilute the concentration, and the like have been adopted.

However, when the coating amount of the magnetic coating material itself is reduced, drying starts before the coating film is sufficiently leveled, and coating defects such as stripes and marking patterns (in the case of the gravure roll coating method) are reduced. Remaining, the yield may be very poor.

Further, when the concentration of the magnetic coating material is reduced, many voids and cracks are formed in the coating film due to evaporation of the solvent, and the filling degree of the ferromagnetic powder decreases.
The coating strength may also be insufficient.

For this reason, as described in JP-A-63-191315, while the lower coating film is in a wet state, an upper coating material is applied on the lower coating film. A method (so-called wet-on-wet coating method) has been proposed.

In the wet-on-wet coating method, a lower layer paint is formed by applying a lower layer paint to form a lower layer paint, and then applying an upper layer paint on the lower layer paint. A sequential wetting system in which the paints for the lower layer and the paint for the upper layer are respectively extruded 2
There is known a simultaneous multi-layer coating method in which an extrusion coater in which two slits are formed close to each other and a lower layer paint and an upper layer paint are simultaneously applied by the extrusion coater.

In such a wet-on-wet coating method, even if the coating amount of the upper layer coating is reduced, the coating is dried at the same time as the lower layer coating. Without having to
The upper magnetic layer is formed with good surface properties. Also,
The adhesion between the lower and upper layers is good, and good running durability is obtained.

However, various studies have been made on the wet-on-wet coating method when both the lower layer paint and the upper layer paint are magnetic paints. There is a lack of knowledge about applying a magnetic paint (upper layer).

For example, depending on the physical properties of the coating material, the upper magnetic layer may be roughened, and the roughened surface may cause a spacing loss, a poor RF envelope, a deterioration in running property and durability,
Dropout may be increased.
Such surface roughness of the upper magnetic layer has no sign when each paint is applied in a single layer, and is a phenomenon that appears for the first time when a multilayer coating is applied.

In particular, such a phenomenon is caused by wet-on-
It has been found that this is likely to occur when a wet coating method is used and the coating thickness of the upper magnetic layer is extremely thin (particularly, 0.3 μm or less). This is because the coating thickness of the upper magnetic layer is too thin, and the effect of evaporation of the solvent therefrom on the surface is apt to occur. In some cases, the surface roughness becomes large and even cracks may occur.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a non-magnetic layer comprising a non-magnetic powder and a binder as a lower layer, and to form a In a magnetic recording medium provided with a magnetic layer composed of a magnetic powder and a binder, the magnetic layer is formed with good surface properties, and the interface between the nonmagnetic layer and the magnetic layer is smooth. An object of the present invention is to provide a magnetic recording medium which is excellent in electromagnetic conversion characteristics, has a good shape of an RF envelope, suppresses dropout, and has excellent running durability, and a method for manufacturing the same.

[0019]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventor has made a non-magnetic layer composed of a non-magnetic powder and a binder into a lower layer, and a magnetic powder and a binder on the lower layer. In a magnetic recording medium provided with a magnetic layer comprising a magnetic agent, at least a predetermined amount of a silicone leveling agent is contained in the magnetic layer to form a coating film by local volatilization of a solvent in a drying process in the magnetic layer. It has been found that non-uniformity (coating stripes, coating defects) can be suppressed.

That is, the present invention relates to a magnetic recording medium comprising a non-magnetic layer comprising a non-magnetic powder and a binder as a lower layer, and a magnetic layer comprising a magnetic powder and a binder provided on the lower layer. The layer contains a silicone leveling agent in a proportion of 0.05 to 1 part by weight (provided that the coating for forming the magnetic layer is 100 parts by weight). (Hereinafter, referred to as the magnetic recording medium of the present invention)
It is related to.

According to the magnetic recording medium of the present invention, the nonmagnetic layer composed of the nonmagnetic powder and the binder is used as the lower layer, and the magnetic layer (upper layer) composed of the magnetic powder and the binder is provided on the lower layer. In the recording medium, at least 0.05 part by weight of a silicone-based leveling agent is added to the magnetic layer.
Parts by weight or less and a specific ratio (provided that the coating for forming the magnetic layer is 100 parts by weight and the silicone-based leveling agent is converted to a pure component). Even if the thickness of the magnetic layer is very thin, 0.3 μm or less, the surface of the magnetic layer is coated with the leveling agent in the applied state (this coated state can be analyzed by microscopic observation), so that the magnetic layer is Is formed with good surface properties without being affected by local volatilization. As a result, while having excellent electromagnetic conversion characteristics, R
It is possible to obtain a magnetic recording medium in which the shape of the F envelope is good, the dropout is suppressed, and the running durability is excellent. However, the above-mentioned conversion to a pure content is a conversion when the silicone-based leveling agent is in a solution form, excluding the solvent.

In the magnetic recording medium of the present invention,
In addition to the magnetic layer, the nonmagnetic layer may also contain a silicone leveling agent. in this way,
When the magnetic layer and the non-magnetic layer contain the silicone-based leveling agent in a predetermined amount, the above-described characteristics are obtained, and the interface between the non-magnetic layer and the magnetic layer may be smooth. Can be

The present invention also provides a process for preparing a non-magnetic coating by dispersing a non-magnetic powder and a binder together with a solvent, and applying the prepared non-magnetic coating on a non-magnetic support to form a non-magnetic coating. Forming a magnetic coating material by dispersing a magnetic powder and a binder together with a solvent, and applying the prepared magnetic coating material on the non-magnetic layer while the non-magnetic layer is in a wet state. Forming a magnetic layer by applying the magnetic paint 100 to at least the magnetic paint out of the non-magnetic paint and the magnetic paint.
The present invention relates to a method for producing a magnetic recording medium (hereinafter, referred to as a production method of the present invention) in which a silicone-based leveling agent is contained in a proportion of 0.05 to 1 part by weight per part by weight.

According to the production method of the present invention, a step of preparing a non-magnetic paint by dispersing a non-magnetic powder and a binder together with a solvent, and applying the prepared non-magnetic paint to a non-magnetic support Forming a non-magnetic layer (lower layer), preparing a magnetic paint by dispersing a magnetic powder and a binder together with a solvent, and disposing the prepared magnetic paint while the non-magnetic layer is in a wet state. Forming a magnetic layer (upper layer) by coating on the non-magnetic layer (so-called wet-on-wet coating). Therefore, even if the thickness of the magnetic layer is reduced to 0.3 μm or less, for example, Since the magnetic paint is dried at the same time as the non-magnetic paint (ie, even if the amount of the magnetic paint applied is reduced), the magnetic paint is dried before it is sufficiently flattened (leveled). Not good The magnetic layer can be formed, may be adhesion between the nonmagnetic layer and the magnetic layer, it is possible to obtain a good running durability having a a surface property.

[0025] In addition, at least a specific proportion (silicone leveling agent) of not less than 0.05 part by weight and not more than 1 part by weight of a silicone-based leveling agent per 100 parts by weight of the magnetic coating material in at least the magnetic coating material of the non-magnetic coating material and the magnetic coating material. (Percentage of pure leveling agent)
Even with such a small amount of addition, the silicone-based leveling agent is effectively unevenly distributed on the surface of the coating film (particularly, a magnetic coating film), and the local volatilization of the solvent is appropriately suppressed. Suppressing uniformity, the magnetic layer can be formed with good surface properties, and has excellent electromagnetic conversion characteristics,
It is possible to manufacture a magnetic recording medium that has a good RF envelope shape, suppresses dropout, and has excellent running durability.

As will be described later in detail, the silicone-based leveling agent typically contains a modified polysiloxane. In the magnetic recording medium of the present invention and the production method of the present invention, a known leveling agent is used. Various silicone leveling agents can be used. Further, since the silicone-based leveling agent has a very low surface tension, even if added in a small amount, it is effectively unevenly distributed on the surface of the coating film, the local volatilization of the solvent is appropriately suppressed, and the coating film after drying is not properly coated. It is considered that uniformity can be suppressed.

In the magnetic recording medium of the present invention and the production method of the present invention, the silicone-based leveling agent is contained in a proportion of 0.05 to 1 part by weight per 100 parts by weight of the magnetic paint. .1 part by weight or more, 0.5
It is preferable that the content is not more than part by weight. If the content of the silicone leveling agent exceeds 1 part by weight, the surface roughness R
a and the RF envelope are improved, but since the content is too large, the silicone-based leveling agent deteriorates the dispersion of the magnetic paint and the surface of the magnetic layer may be roughened, and the electromagnetic conversion characteristics may be deteriorated and the dropout may occur. Is thought to increase. When the content of the silicone-based leveling agent is 0.0
If the amount is less than 5 parts by weight, the content is too small, so that a sufficient effect cannot be obtained.

When a silicone-based leveling agent is contained in the non-magnetic layer in addition to the magnetic layer, the silicone-based leveling agent is added to the non-magnetic coating in an amount of 0.1% by weight, as in the case of the magnetic layer. It is preferable to contain it in a proportion of not less than 05 parts by weight and not more than 1 part by weight, more preferably not less than 0.1 part by weight and not more than 0.5 part by weight for the same reason as described above. However, in this case, since the leveling agent is also present at the interface between the lower non-magnetic layer and the upper magnetic layer, it is possible to further reduce the disturbance at the interface between the two layers. It is also advantageous for improvement.

It has been conventionally known that a silicone-based lubricant such as silicone oil is contained in a magnetic layer. However, the silicone oil or the like is a lubricant.
It is added for the purpose of improving the friction characteristics of the magnetic layer, has no effect of suppressing the surface roughness of the magnetic layer, and cannot be expected to improve the electromagnetic conversion characteristics, the RF envelope, the running durability, and the like. Therefore, it goes without saying that the conventional lubricant is different from the silicone leveling agent of the present invention.

Generally, in order to prepare a multilayer-coated magnetic recording medium having a non-magnetic layer and a magnetic layer on a non-magnetic support by a wet-on-wet coating method, a non-magnetic powder and a binder are used. A non-magnetic coating prepared by dispersing with a solvent is coated on the non-magnetic support, and the magnetic coating prepared by dispersing a magnetic powder and a binder with a solvent is wetted with the non-magnetic layer. During the state, a magnetic layer is formed by coating on the non-magnetic layer.

However, in such a wet-on-wet coating method, the interface between the magnetic layer and the non-magnetic layer is disturbed depending on the composition of each of the paints, and
Surface roughness occurs on the surface of the magnetic layer, thereby deteriorating electromagnetic conversion characteristics of a magnetic recording medium (for example, a magnetic tape, a magnetic disk, etc.), RF envelope defect, running and durability deterioration, increasing dropout, and the like. May be caused.

Such disorder of the interface and surface roughness of the magnetic layer may be caused by local volatilization of the solvent of the coating film for the magnetic layer in the process of drying the magnetic layer in the process of manufacturing the magnetic recording medium. It is presumed that uniformity (generation of streaks, defects, cracks, etc.) is the main cause.

Therefore, according to the manufacturing method of the present invention, as described above, local drying (solvent volatilization) in the drying process of the magnetic layer is suppressed, and the interface between the magnetic layer and the non-magnetic layer is suppressed. In order to bring the surface of the magnetic layer into a good state,
At least 0.05 part by weight or more and 1 part by weight or less of a silicone-based leveling agent per 100 parts by weight of the magnetic paint is added to the magnetic layer, and then applied on the non-magnetic layer to obtain each of the above properties. Can be improved.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the magnetic recording medium of the present invention and the manufacturing method of the present invention, the thickness of the magnetic layer is 0.3 μm.
The following is preferred. In addition, it is possible to sufficiently reduce coating streaks and coating defects after such thinning.

As described above, when the thickness of the magnetic layer is very thin, that is, 0.3 μm or less, self-demagnetization loss at the time of recording and thickness loss at the time of reproduction, especially in a high-density recording area (short-wavelength recording area). And the electromagnetic conversion characteristics are improved. The thickness of the magnetic layer is more preferably 0.1 to 0.3 μm, and if the thickness of the magnetic layer exceeds 0.3 μm, a thickness loss or the like particularly occurs during short-wavelength recording, and The conversion characteristics may be deteriorated. For example, a magnetic recording medium (for example, home digital video: D
VC) may be insufficient.

In the magnetic recording medium of the present invention and the manufacturing method of the present invention, it is preferable that the silicone-based leveling agent is a modified polysiloxane.

As described above, since the silicone-based leveling agent has a very small surface tension, it is effectively unevenly distributed on the surface of the coating film even when added in a small amount, and moderately suppresses local volatilization of the solvent, and It is considered that the non-uniformity of the subsequent coating film can be suppressed.

The silicone-based leveling agent includes:
Trade names ST83PA, ST86PA, SH200 / 100c manufactured by Toray Dow Corning Silicone Co., Ltd.
s, DC3PA, DC11PA, SH21PA, SH2
8PA, ST90PA, etc., and product names KP322, KP323, KP321, KP manufactured by Shin-Etsu Chemical Co., Ltd.
324, KP326, KP340, KP341 and the like can be used.

As the physical properties of these silicone leveling agents, viscosity, surface tension, solvent selectivity (compatibility with a solvent), and further, molecular weight are important.
Table 1 below shows an example of each property value of each of the silicone-based leveling agents.

[0040]

[Table 1]

Here, the silicone-based leveling agent used in the magnetic recording medium of the present invention and the manufacturing method of the present invention preferably has a surface tension of about 20 to 28 dyne / cm (25 ° C.). However, in Table 1 above, KP
Physical properties other than the viscosity of the silicone-based leveling agents such as 322, KP323, KP321, and KP324 are unknown.

In the manufacturing method of the present invention, it is preferable that the magnetic layer and the non-magnetic layer are formed using an extrusion coater.

As will be described in detail later, in addition to the extrusion coater, wet-on-wet coating can be performed by various methods. However, due to productivity and simplicity of the manufacturing apparatus, simultaneous coating using an extrusion coater can be performed. It is preferable to form by a coating method.

In the magnetic recording medium of the present invention and the manufacturing method of the present invention, specific materials for the magnetic layer and the non-magnetic layer include the following.

First, the magnetic layer is mainly composed of a ferromagnetic powder and a binder.
γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-attached γ
Ferrites represented by Fe ₂ O ₃ , CrO ₂ and magnetite, ie, Fe ₃ O ₄ , Fe containing Co;
₃ O ₄ , Co-coated Fe ₃ O _{4 and the} like.

Among these ferrites, those having a plate shape and having an easy axis of magnetization in a direction perpendicular to the plate surface are suitable as ferromagnetic powders. Ferrite having such an easy axis of magnetization includes hexagonal ferrite.

The hexagonal ferrite includes barium ferrite and strontium ferrite, and a part of the iron element is replaced by another element (for example, Ti, Co, Zn, In, Mn).
n, Ge, Nb, etc.). In addition,
Among the hexagonal ferrites, barium ferrite is particularly preferable, and further, barium ferrite in which a part of Fe is substituted by at least Co and Zn, and having an average particle diameter (diagonal length of the plate surface of the hexagonal ferrite) ) Is 3
The sheet ratio (value obtained by dividing the length of the diagonal line of the plate surface of hexagonal ferrite by the plate thickness) is 2.0 to 10.0,
Those having a coercive force Hc of 450 to 1500 Oe are preferred.

As the ferromagnetic powder, a metal magnetic powder may be used. Examples of the metal magnetic powder include metal powders such as Fe and Co, Fe-Al-based, Fe-Al-Ni-based,
Fe-Al-Zn system, Fe-Al-Co system, Fe-Al
-Ca-based, Fe-Ni-based, Fe-Ni-Co-based, Fe-
Ni-Si-Al-Mn system, Fe-Ni-Si-Al-
Zn-based, Fe-Al-Si-based, Fe-Ni-Zn-based, F
e-Ni-Mn system, Fe-Ni-Si system, Fe-Mn-
An alloy powder containing Fe, Ni, Co, or the like as a main component, such as a Zn-based, Fe-Co-Ni-P-based, or Ni-Co-based powder, may be used.

Of these, Fe-based magnetic powders have excellent electrical characteristics. In terms of corrosion resistance and dispersibility, Fe
-Al system, Fe-Al-Ca system, Fe-Al-Ni system,
Fe-Al-Zn system, Fe-Al-Co system, Fe-Ni
-Si-Al-Zn system, Fe-Ni-Si-Al-Mn
Fe-Al-based alloy powders such as iron-based alloys are preferred.

The shape of the metal magnetic powder has an average major axis length of 0.5 μm or less, preferably 0.01 to 0.4 μm.
m, more preferably 0.01 to 0.3 μm, and an axial ratio (average major axis length / average minor axis length) of 12 or less, preferably 10 or less. For example, it is an Fe—Al ferromagnetic metal powder (Fe: Al weight ratio = 100: 5) having an average major axis length of 0.16 μm and a coercive force Hc of 1580.
Oe and those having a saturation magnetization σs of 120 emu / g exhibit very excellent characteristics. The average major axis length and average minor axis length can be determined by observation with a transmission electron microscope or the like.

As described above, as the ferromagnetic powder, an oxide magnetic powder or a metal magnetic powder can be used, and in any case, the saturation magnetization (σs) is preferably 70 emu / g or more. When the saturation magnetization is less than 70 emu / g,
Sufficient electromagnetic conversion characteristics may not be obtained. In order to improve the recording / reproducing ability in a high density recording area, BE
The specific surface area by the T method is preferably 45 m ² / g or more.

Next, typical examples of the binder include polyurethane resins, polyester resins, and vinyl chloride resins such as vinyl chloride copolymers.

These resins are -SO ₃ M, -OSO
₃ M, —COOM, —PO (OM ′) ₂ (where M represents a hydrogen atom or an alkali metal atom such as Na, K, Li, and M ′ represents a hydrogen atom or an alkali metal atom such as Na, K, Li, etc.) , Which represents an alkyl group) and a sulfopetine group. These polar groups have the effect of improving the dispersibility of the ferromagnetic powder, and the content is 0.1 to
It is preferably 8.0 mol%, more preferably 0.2 to 6.0 mol%. When the content of the polar group is less than 0.1 mol%, the dispersibility of the magnetic powder is reduced. Conversely, the content is 8.0
If it exceeds mol%, the magnetic paint tends to gel.
The weight average molecular weight of the resin is 15,000 to 50,
It is preferably in the range of 000.

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

The polyester resin can be synthesized by reacting a polyol with a polybasic acid. It should be noted that a polyester into which another polar group has been introduced can also be synthesized by a known method.

The polyurethane resin can be synthesized by a reaction between a polyol and a polyisocyanate. As this polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. When a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

These resins may be used alone or in a combination of two or more. For example,
When a mixture of polyurethane and / or polyester and a vinyl chloride resin is used, the weight ratio is 90:10.
It is good to be in the range of 10 to 90, preferably 70:30 to 30:70.

Further, the following resin was added to 50% by weight of the total binder.
The following usage amount may be used together.

That is, as the resin used in combination, a vinyl chloride-vinyl acetate copolymer having a weight average molecular weight of 10,000 to 200,000, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer, Butadiene-acrylonitrile copolymer, polyamide resin,
Polyvinyl butyral, cellulose derivatives (nitrocellulose, etc.), styrene-butadiene copolymer, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, various synthetic rubber resins And the like.

As the binder, the above-mentioned resins can be used. The amount of the binder to be mixed with the magnetic layer is 8 to 25 with respect to 100 parts by weight of the ferromagnetic metal powder.
Preferably, the amount is 10 parts by weight, more preferably 10 to 20 parts by weight.

For the purpose of improving the running durability and the like of the medium, the magnetic layer usually contains abrasives, lubricants, hardeners (durability improvers), An additive such as an agent, an antistatic agent and a conductive fine powder may be added.

As the abrasive, JP-A-4-214218
A solid powder as described in JP-A No. 2-211 can be used. The average particle size of the abrasive is 0.05 μm to 0.6 μm, preferably 0.05 μm to 0.5 μm, and more preferably 0.1 μm to 0.5 μm.
It is from 0.05 μm to 0.3 μm. The amount of the abrasive added is 3 to 20 parts by weight (based on 100 parts by weight of magnetic powder), preferably 5 to 15 parts by weight, more preferably 5 to 1 part by weight.
It is suitably 0 parts by weight.

As the lubricant, fatty acids and fatty acid esters are used alone or in combination. The fatty acid may be a monobasic acid or a dibasic acid, and has a carbon number of 6 to
30 is preferable, and it is more preferable that it is 12-22.

The addition amount of these fatty acids and fatty acid esters is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder.
When the amount of the fatty acid is less than 0.2% by weight, the running property of the medium is not sufficiently improved. When the amount exceeds 10% by weight, the fatty acid exudes to the surface of the magnetic layer or the output decreases. Is more likely to occur. On the other hand, if the amount of the fatty acid ester is less than 0.2% by weight, still durability is particularly insufficient. If it exceeds 10% by weight, the fatty acid ester is likely to exude to the surface of the magnetic layer or the output is liable to decrease.
When a fatty acid and a fatty acid ester are used in combination, the ratio of the fatty acid to the fatty acid ester is 10:90 to 9 by weight.
0:10 is preferred.

A known lubricant may be used in combination with the above fatty acids and fatty acid esters. Examples of the lubricant used in combination include silicone oil, carbon fluoride, fatty acid amide, olefin oxide and the like.

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

As the dispersant, JP-A-4-214218
Compounds such as those described in the publication can be used. These dispersants are suitably used in the range of 0.5 to 5% by weight based on the magnetic powder.

As the antistatic agent, JP-A-4-2142
Surfactants as described in JP-A-18 can be used. The addition amount of these antistatic agents is preferably in the range of 0.01 to 40% by weight based on the binder. In addition,
A conductive fine powder may be added as an antistatic agent. Examples of the conductive fine powder include metal particles such as carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, silver inorganic compounds, copper powder, zinc oxide, barium sulfate,
Pigment such as metal oxide such as titanium oxide is coated with a conductive substance such as tin oxide film or antimony solid solution tin oxide film. The average particle diameter of these conductive fine powders is 5 to 700 nm, preferably 5 to 700 nm.
It is preferably 00 nm. The amount of the conductive fine powder to be added is 1 to 20 parts by weight, preferably 2 to 7 parts by weight, per 100 parts by weight of the magnetic powder.

The non-magnetic layer is mainly composed of a non-magnetic powder and a binder.

First, non-magnetic powders include carbon black, graphite, TiO ₂ , barium sulfate, 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
-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, garnet, silica, silicon nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, Diatomaceous earth, dolomite and the like can be mentioned. this house,
In particular, carbon black, CaCO ₃ , TiO ₂ , barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeO
Inorganic powders such as OH and Cr ₂ O ₃ are preferred.

These non-magnetic powders may be surface-treated with a Si compound and / or an Al compound. The use of the surface-treated nonmagnetic powder improves the surface properties of the magnetic layer. In addition, surface treatment is Si,
Al content is 0.1 to 10% by weight based on the nonmagnetic powder
It is preferable to carry out the following.

The shape of the nonmagnetic powder is desirably acicular. By using needle-shaped non-magnetic powder,
The smoothness of the surface of the nonmagnetic layer is improved, and as a result, the surface of the magnetic layer laminated on this layer also becomes smooth. The major axis length, minor axis diameter and axial ratio of nonmagnetic powder (major axis diameter / minor axis diameter)
Is preferably in the following range. That is, the major axis diameter of the non-magnetic powder is 0.50 μm or less, preferably 0.40 μm or less, and more preferably 0.30 μm or less.
The short axis diameter is 0.10 μm or less, preferably 0.00 μm.
The thickness is preferably 8 μm or less, more preferably 0.06 μm or less. The axial ratio (major axis diameter / minor axis diameter) is 2 to 20,
It is preferably 5 to 15, more preferably 5 to 10. The specific surface area is 10 to 250 m ² / g, preferably 20 to 150 m ² / g, more preferably 30 to 1 m ² / g.
It is preferably 00 m ² / g. By using a non-magnetic powder having a major axis diameter, a minor axis diameter, an axial ratio, and a specific surface area as described above, the surface property of the lower non-magnetic layer is improved, and the surface property of the upper magnetic layer laminated thereon is improved. Will also be in good condition.

The mixing amount of the non-magnetic powder in the non-magnetic layer is 50 to 9 with respect to the total amount of all the components constituting the non-magnetic layer.
Suitably, it is 9% by weight, preferably 60-95% by weight, more preferably 70-95% by weight. By setting the mixing amount of the non-magnetic powder in this range, the surface properties of the non-magnetic layer and thus the magnetic layer are improved.

As the binder, any resin that can be used for the magnetic layer can be used. The mixing amount of the binder is 5 to 150 parts by weight, preferably 10 to 120 parts by weight, based on 100 parts by weight of the nonmagnetic powder.

Further, various additives exemplified for the magnetic layer can also be added to the non-magnetic layer.

In order to form a nonmagnetic layer (lower layer) and a magnetic layer (upper layer) using the above-mentioned raw materials, first, a lower layer nonmagnetic coating and an upper layer magnetic coating are prepared.

The magnetic paint for the upper layer was prepared by kneading various additives such as the ferromagnetic powder, binders and dispersants, lubricants, abrasives, and antistatic agents exemplified above together with a solvent, to thereby prepare a high-concentration magnetic paint. Thereafter, the high-concentration magnetic paint can be prepared by diluting and dispersing it. In addition, the non-magnetic paint for the lower layer is prepared by kneading various additives such as the non-magnetic powder, binder and dispersant, lubricant, abrasive, and antistatic agent shown above together with a solvent to form a high-concentration non-magnetic paint. After that, the high-concentration non-magnetic paint can be prepared by diluting and dispersing.

As the solvent for forming the coating, those usually used in this type of magnetic recording medium, for example, those disclosed in
What is described in 214218 gazette is used. This solvent may be used alone or as a mixture of two or more.

As the kneading and dispersing machine, any of those described in, for example, JP-A-4-214218 can be used. In particular, since a power consumption load of 0.05 to 0.5 kW (per kg of magnetic powder) can be provided,
A pressure kneader, open kneader, continuous kneader, two-roll mill, and three-roll mill are suitable.

The non-magnetic layer and the magnetic layer are formed by applying the lower non-magnetic paint and the upper magnetic paint thus prepared on a non-magnetic support and drying.

However, at the time of the above-mentioned application, the above-mentioned magnetic paint is applied after a silicone leveling agent is added at a ratio of 0.05 to 1 part by weight in terms of a pure component based on the weight of the paint. This silicone leveling agent may be added to each layer or may be added only to the magnetic layer.

Here, as the non-magnetic support, for example,
Polyethylene terephthalate, polyethylene-2,6-
Examples include polyesters such as naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide, aramid resin and polycarbonate. These nonmagnetic supports may have a single-layer structure or a multilayer structure. Further, for example, a surface treatment such as a corona discharge treatment may be performed.

The thickness of the nonmagnetic support is not particularly limited. For example, when the medium is a film or a sheet,
Suitably, it is 2 to 100 μm, preferably 3 to 50 μm. In the case of a disk or card, 30
The thickness is about μm to 10 mm, and in the case of a drum shape, it is appropriately selected according to the design of a recorder or the like.

Here, for forming the magnetic layer and the non-magnetic layer according to the present invention, for example, a coating film forming system as shown in FIG. 6 can be used.

That is, in this coating film forming system,
A non-magnetic support 11 on which a coating film (a non-magnetic layer and a magnetic layer) is formed is transported from a supply roll 13 to a take-up roll 12 in a direction indicated by an arrow D in FIG. Along the coating device 14, an orienting magnet 15, a dryer 16 and a calender device 17 are arranged in this order.

In such a coating film forming system, first, the upper magnetic coating material and the lower non-magnetic coating material are applied on the non-magnetic support 11 by the coating device 14 in a multi-layered manner.

As shown in FIG. 7A, the coating device 14 includes a lower extruder coater 18 for applying a lower layer (non-magnetic layer: the same applies hereinafter) paint, and an upper layer (magnetic layer:
An upper layer extrusion coater 19 for applying a coating material for the lower layer is the same as the upper layer extrusion coater 19 and the lower layer extrusion coater 18.
Are arranged and configured so as to be on the introduction side of the nonmagnetic support 11.

The lower-layer extrusion coater 18 and the upper-layer extrusion coater 19 have slits 20 and 22 formed at the tips thereof for extruding the paint, and the paint is supplied to the back side of the slits 20 and 22. Paint pools 21 and 23 are provided. In such extrusion coaters 18 and 19, the paint supplied to the paint pools 21 and 23 is pushed out to the tip of the coater through the slits 20 and 22.

On the other hand, the nonmagnetic support 11 to which the paint is applied
Is transported from the lower layer extrusion coater 18 to the upper layer extrusion coater 19 in the direction of arrow D along the tip surfaces of the lower layer extrusion coater 18 and the upper layer extrusion coater 19.

The non-magnetic support 1 thus transported
First, when passing through the lower layer extrusion coater 18, the slit section 20 of the lower layer extrusion coater 18 is formed.
The lower layer coating material extruded from is applied to the surface to form the lower layer coating film 24. Then, when passing through the upper layer extrusion coater 19, the upper layer coating material extruded from the slit portion 22 of the upper layer extrusion coater 19 is applied onto the wet lower layer coating film 24, and the lower layer coating film 24 and the upper layer coating film are coated. The films 25 are sequentially formed.

Note that these extruder coaters 18, 19
The supply of the coating material may be performed through an in-line mixer.

The lower coating film and the upper coating film formed on the non-magnetic support as described above are sequentially conveyed to the magnet 15 for orientation, the dryer 16 and the calender 17.

In the magnet 15 for orientation, the upper coating film (magnetic coating film) is subjected to magnetic field orientation treatment. As the magnet 15 for orientation, a magnet for longitudinal orientation or a magnet for vertical orientation is appropriately selected depending on the type of magnetic powder contained in the upper coating film.
The magnetic field of these orienting magnets is desirably about 20 to 10,000 Gauss.

In the dryer 16, the lower layer coating film and the upper layer coating film can be dried by, for example, hot air from nozzles arranged above and below the dryer 16. At this time, the drying conditions include a temperature of about 30 to 120 ° C. and a drying time of about 0.1 to 1
It is preferable to set the time to about 0 minutes.

Then, the lower layer coating film and the upper layer coating film that have passed through the dryer 16 are further guided to a calender 17 and subjected to a surface smoothing treatment. In the conditions of the surface smoothing treatment by the calender device 17, the temperature, the linear pressure, the transport speed, and the like are important. Here, the temperature is 50 to 140 ° C., the linear pressure is 50 to 1000 kg / cm ² , and the transport speed is 20.
Preferably it is ~ 1000 m / min. If these conditions are not satisfied, the surface properties of the upper layer may be impaired.

As described above, the lower non-magnetic layer and the upper magnetic layer are formed. In this coating film forming process, at least a silicone-based leveling agent is added to the above magnetic paint in terms of a pure content with respect to the paint weight. Since it is applied after being added at a ratio of 0.05 part by weight or more and 1 part by weight or less, nonuniformity of the coating film due to local solvent volatilization in the drying process in the upper magnetic layer can be suppressed. Therefore, the upper magnetic layer is formed with good surface properties, and the adhesion between the lower and upper layers is also good.

In this coating system, the lower layer paint and the upper layer paint are applied by separate coaters. However, as shown in FIG. 7 (B), the lower layer extrusion coater and the upper layer extrusion coater are separated. May be used as an extrusion coater 26 in an integrated form.

Furthermore, in addition to the extrusion coater, a slide coater, a spray coater, a reverse roll, a gravure roll, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnated coater,
A transfer roll coater, kiss coater, cast coater or the like may be used. At this time, the method of applying the lower layer paint and the upper layer paint may be the same or different. Therefore, for example, a slide coater and an extrusion coater can be combined, or a spray coater and an extrusion coater can be combined to apply the upper layer paint and the lower layer paint, respectively.

Further, in the above configuration, the lower layer non-magnetic paint and the upper layer magnetic paint are sequentially applied. However, an extrusion coater having two slits formed close to each other is used. The paint and the upper layer paint may be applied simultaneously.

That is, as shown in FIG. 7 (C), the extrusion coater 27 used in the simultaneous multi-layer coating method has two slit portions (a lower layer slit portion 28 and an upper layer slit portion 30) at the tip of which the paint is extruded. On the back side of the two slit portions 28 and 30, a lower layer paint reservoir 29 and an upper layer paint reservoir 31 to which a lower layer paint and an upper layer paint are supplied, respectively, are provided. In the extrusion coater 27, the lower layer paint and the upper layer paint supplied to the paint pools 29 and 31 are supplied to the slit portions 28 and
It is extruded through 30 to the tip of the coater. On the other hand, the nonmagnetic support 11 to which the coating material is applied is conveyed along the distal end surface of the extrusion coater from the lower layer slit section 28 to the upper layer slit section 30 in the direction of arrow D in the figure.

The non-magnetic support 1 thus transported
1 has a lower layer slit 28 and an upper layer slit 3
0, the lower-layer paint extruded from the lower-layer slit portion 28 is applied, and the upper-layer paint extruded from the upper-layer slit portion 30 is applied on the lower-layer paint. The coating film 24 and the magnetic coating film 25 are simultaneously formed.

The magnetic film on which the lower non-magnetic layer and the upper magnetic layer are formed as described above is thereafter subjected to a burnishing treatment or a blade treatment as necessary to obtain a desired medium shape. It becomes a magnetic recording medium.

Here, in the extrusion coater described above, the tip of the slit may be in contact with the non-magnetic support or may be non-contact.

Further, according to the magnetic recording medium of the present invention and the manufacturing method of the present invention, the nonmagnetic layer and the magnetic layer containing the silicone-based leveling agent are formed on the nonmagnetic support 11 by the coating apparatus 14 shown in FIG. When the silicone-based leveling agent is applied in multiple layers, the surface tension of the silicone-based leveling agent is small, so that a film 5 of the silicone-based leveling agent is formed on the magnetic layer 3 as shown in FIG. It is considered that the coating 5 appropriately suppresses local volatilization of the solvent and can suppress nonuniformity of the dried coating film (particularly, the magnetic layer 3).

As the medium shape, any shape generally used in magnetic recording media such as a tape shape, a film shape, a sheet shape, a card shape, a disk shape and a drum shape can be adopted.

The magnetic recording medium manufactured in this manner has excellent electromagnetic conversion characteristics and a good RF envelope shape since the upper layer has good surface properties.
Also, dropout is suppressed. Further, since the adhesiveness between the lower and upper layers is high, film peeling hardly occurs, high film strength is obtained, and excellent running durability is obtained.

In order to improve the electromagnetic conversion characteristics in the high-density recording area, it is desirable that the upper magnetic layer has a thickness of 0.3 μm or less, preferably 0.1 to 0.3 μm. If the thickness of the upper magnetic layer exceeds 0.3 μm, the electrical characteristics may be deteriorated, and for example, it may be insufficient as a medium applied to a digital recording system.

The above is a description of the manufacturing process of the magnetic recording medium having the basic structure. Further, a back coat layer may be provided on the surface where the lower and upper layers of the non-magnetic support are not provided, or the lower layer and the non-magnetic support may be combined with each other. An undercoat layer may be provided between them. These back coat layer and undercoat layer can be formed according to a usual method.

[0109]

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

In this example, a non-magnetic layer was formed as a lower layer on a non-magnetic support made of polyethylene terephthalate, and a magnetic recording medium (magnetic tape) having a magnetic layer provided on this lower layer was manufactured. And its properties were evaluated.

Table 2 below shows the amount (parts by weight) of the silicone-based leveling agent added to the weight of the magnetic paint for the upper layer and the non-magnetic paint for the lower layer in terms of the pure content.

Example 1 First, the respective components of the magnetic paint for the upper layer and the non-magnetic paint for the lower layer were measured according to the following composition, and kneaded and dispersed using a kneader and a sand mill, respectively. A non-magnetic coating for the lower layer was prepared.

<Magnetic paint for upper layer> 100 parts by weight of ferromagnetic iron fine powder (coercive force Hc: 1600 Oe, specific surface area by BET method: 55 m ² / g, major axis diameter: 0.25 μm, needle ratio: 10, saturation Magnetization amount σs: 120 emu / g) Binder: Potassium sulfonate group-containing vinyl chloride resin 14 parts by weight (trade name: MR-110, manufactured by Zeon Corporation) Sodium sulfonate group-containing polyurethane resin 6 parts by weight (manufactured by Toyobo Co., Ltd.) Name UR-8700) α-alumina 5 parts by weight Myristic acid 1 part by weight butyl stearate 1 part by weight Solvent 350 parts by weight (mixed solvent having a composition of methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1)

<Nonmagnetic paint for lower layer> 100 parts by weight of α-Fe ₂ O ₃ (specific surface area by BET method: 52 m ² / g, major axis diameter: 0.15 μm, needle ratio: 6) Binder: sulfonic acid Potassium group-containing vinyl chloride resin 14 parts by weight (trade name: MR-110 manufactured by Zeon Corporation) Sodium sulfonate group-containing polyurethane resin 6 parts by weight (trade name: UR-8700 manufactured by Toyobo Co., Ltd.) 1 part by weight butyl stearate Solvent 220 Parts by weight (a mixed solvent having a composition of methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1)

A silicone leveling agent (Dow Corning Toray) was added to the magnetic paint for the upper layer thus prepared.
Silicone Co., Ltd. product name ST83PA) paint 1
1 part by weight in terms of a pure content is added to 00 parts by weight (hereinafter the same), and a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) is added to each of the magnetic paint for the upper layer and the non-magnetic paint for the lower layer. 5 parts by weight were added to obtain a magnetic paint for the upper layer and a non-magnetic paint for the lower layer.

Next, using the coating film forming system shown in FIG. 6, a wet-on-wet coating method was used to coat the non-magnetic paint and the magnetic material on a non-magnetic support made of polyethylene terephthalate having a thickness of 7.5 μm. The coating is applied in multiple layers, and the magnetic field orientation treatment is performed while the coating film is in an undried state (wet state). Then, the surface is smoothed by drying and calendering to form a lower non-magnetic layer and an upper magnetic layer. did. The thickness (dry film thickness) of the lower non-magnetic layer was 1.5 μm and that of the upper magnetic layer was 0.15 μm.

Further, a coating for a back coat layer having the following composition was applied to the surface of the non-magnetic support made of polyethylene terephthalate opposite to the side on which the lower non-magnetic layer and the upper magnetic layer were formed, and dried. Then, a back coat layer having a thickness of 0.8 μm was formed by performing a surface smoothing treatment using a calender to obtain a raw material for a magnetic tape having a wide width.

<Coating for Back Coat Layer> Carbon black (average particle size 26 nm) 40 parts by weight Barium sulfate (average particle size 300 nm) 10 parts by weight Nitrocellulose 25 parts by weight Polyurethane resin 25 parts by weight (trade name of Nippon Polyurethane Industry Co., Ltd. N-2301) Polyisocyanate compound 10 parts by weight (Coronate L, trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.) Solvent 900 parts by weight (Mixed solvent having composition of methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1)

The magnetic tape raw material thus obtained was cut into a tape width of 8 mm to produce a magnetic tape.

Examples 2 to 12 In the same manner as in Example 1 except that the silicone leveling agents of the type and amount shown in Table 2 below were used as the silicone leveling agents to be added to the magnetic paint for the upper layer. A magnetic tape was produced.

Examples 13 to 15 Magnetic tapes were prepared in the same manner as in Example 1 except that a silicone-based leveling agent was added to the non-magnetic paint for the lower layer in addition to the magnetic paint for the upper layer. The amount of the silicone leveling agent added to each paint is shown in Table 2 below.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that no silicone-based leveling agent was added to the magnetic paint for the upper layer and the non-magnetic paint for the lower layer.

Comparative Examples 2 to 9 As the silicone-based leveling agent added to the upper layer magnetic paint, those shown in Table 2 below were used. That is, the amount of the silicone-based leveling agent added to the upper layer magnetic paint was: A magnetic tape was produced in the same manner as in Example 1 except that the amount was less than 0.05 part by weight or more than 1 part by weight based on the paint weight.

Comparative Example 10 In Comparative Example 1 in which no silicone-based leveling agent was added to the magnetic paint for the upper layer and the non-magnetic paint for the lower layer, a silicone-based lubricant (silicone oil) conventionally used as a lubricant was used. Parts by weight are added to the upper layer magnetic paint.

Table 2A—Silicone Level Silicone based on parts by weight of paint Type of ring agent Addition amount in terms of pure content Surface tension of leveling agent (brand name) (parts by weight) (dyne / cm, 25 ° C) ─────────────────── ───────────────── Example 1 ST 86 PA (* 1) 1 (only upper layer) 25.7 Example 2 ST 86 PA (* 1) 0.5 (only upper layer) 25.7 Example 3 ST 86 PA (* 1) 0.05 (only upper layer) 25.7 Example 4 ST 83 PA (* 1) 1 (only upper layer) 21.1 Example 5 ST 83 PA (* 1) 0.5 (only upper layer)
21.1 Example 6 ST 83 PA (* 1) 0.05 (only upper layer) 21.1 Example 7 KP 322 (* 2) 1 (only upper layer) ── Example 8 KP 322 (* 2) 0.5 (only upper layer) 実 施 Example Example 9 KP 322 (* 2) 0.05 (only upper layer) ── Example 10 KP 323 (* 2) 1 (only upper layer) ── Example 11 KP 323 (* 2) 0.5 (only upper layer) ── Example 12 KP 323 (* 2) 0.05 (upper layer only) ── Example 13 ST 86 PA (* 1) 0.5 (upper layer), 1 (lower layer) 25.7 Example 14 ST 86 PA (* 1) 0.5 (upper layer), 0.5 (upper layer) Lower layer) 25.7 Example 15 ST 86 PA (* 1) 0.5 (upper layer), 0.05 (lower layer) 25.7 mm ───────── * 1: Dow Corning Toray Silicone Co., Ltd. * 2: Shin-Etsu Chemical Co., Ltd. * However, the surface tension of the silicone leveling agents of Examples 7 to 12 is unknown. .

Table 2B—Silicone level Silicone based on parts by weight of paint Type of ring agent Addition amount in terms of pure content Surface tension of leveling agent (brand name) (parts by weight) (dyne / cm, 25 ° C) ─────────────────── ───────────────── Comparative Example 1 No additive 0 ── Comparative Example 2 ST 86 PA (* 1) 2 (only upper layer) 25.7 Comparative Example 3 ST 86 PA (* 1 ) 0.01 (only upper layer) 25.7 Comparative Example 4 ST 83 PA (* 1) 2 (only upper layer) 21.1 Comparative Example 5 ST 83 PA (* 1) 0.01 (only upper layer) 21.1 Comparative Example 6 KP 322 (* 2) 2 (only upper layer) ─
比較 Comparative Example 7 KP 322 (* 2) 0.01 (only upper layer) ── Comparative Example 8 KP 323 (* 2) 2 (only upper layer) 比較 Comparative Example 9 KP 323 (* 2) 0.01 (only upper layer) 比較 Compare Example 10 ──── ──── ── ──────────────────────────────────── * 1 : Manufactured by Dow Corning Toray Silicone Co., Ltd. * 2: manufactured by Shin-Etsu Chemical Co., Ltd. * However, the surface tension of the silicone leveling agents of Comparative Examples 6 to 9 is unknown.

With respect to the magnetic tape thus manufactured, the surface roughness, surface roughness Ra, electromagnetic conversion characteristics, RF envelope, and the number of dropouts were measured. In addition,
The measuring method is as follows.

Surface roughness: The surface of the magnetic tape was observed using a differential interference microscope. At this time, the case where the surface was judged to be fairly smooth was evaluated as ○, the case where it was judged that the surface was slightly rough was evaluated as Δ, and the case where it was judged that the surface was fairly rough was evaluated as ×.

Surface roughness Ra (nm): JIS B 06
It is the center line average roughness Ra defined by 01. The surface roughness Ra was measured using a tally step roughness meter manufactured by Taylor Hopson. The measurement conditions were stylus 2.5
× 0.1 μm, needle pressure 2 mg, cut-off filter 0.33 Hz, measurement speed 2.5 μm / s, reference length 0.5 mm. In the roughness curve,
Irregularities of 0.01 μm or more were cut.

Electromagnetic conversion characteristics: Chroma S / N (C-S /
N) and Lumi S / N (LS / N) were evaluated. The chroma S / N was measured by using a noise meter (manufactured by Shibasoku) to determine the difference in S / N between the reference tape (manufactured by Sony Corporation) and the sample tape in a 100% chroma signal. Lumi S / N was measured using a noise meter (manufactured by Shibasoku Co., Ltd.)
S / N between reference tape (Sony) and sample tape
Was determined by determining the difference between These measurement data are
It was recorded as a relative value when the value on a reference tape (manufactured by Sony Corporation) was 1 dB.

RF Envelope: A sample tape of 8
The vehicle was run on a millideck (trade name: S-550, manufactured by Sony Corporation), the RF envelope at that time was projected on an oscilloscope, and evaluation was performed by calculating the ratio between the maximum value and the minimum value of the envelope.

Number of dropouts: The number of dropouts (number of dropouts) of -12 dB / 5 μs detected per minute was measured by a measuring instrument (trade name: VHO1BZ, manufactured by Shibasoku).

The results of these measurements are shown in Table 3 below. FIGS. 1 to 5 show changes in respective properties of the magnetic tapes of Examples 1 to 12 and Comparative Examples 2 to 9 depending on the amount of the silicone leveling agent added.

Table 3A 面 Surface Roughness Surface Roughness CS / N LS / N RF En Dropout Ra (nm) (dB) (dB) Velocity (pcs / min) ───────────────────────────実 施 Example 1 ○ 1.8 0.1 1.3 84 1 Example 2 ○ 2.1 0.9 0.1 84 2 Example 3 ○ 1.8 1.2 1.2 89 2 Example 4 ○ 1.9 0.8 0.8 81 3 Example 5 ○ 1.5 1.1 1.9 81 3 Example 6 ○ 2.9 1 1.5 82 2 Example 7 ○ 1.6 0.8 1.3 81 1 Example 8 ○ 2.2 1.3 0.5 84 3 Example 9 ○ 2.2 0.7 1.1 83 2 Example 10 ○ 1.9 1.2 0.6 81 4 Example Example 11 ○ 2.1 1.2 1.2 85 3 Example 12 ○ 2.7 1.3 0.4 87 4 Example 13 ○ 1.2 1.2 1.1 88 2 Example 14 ○ 1.8 1.3 1.2 89 1 Example 15 ○ 1.9 1.3 1.2 88 2 ────── ───────────────────────────── ─

Table 3B ──────────────────────────────────── Surface Roughness Surface Roughness CS / N LS / N RF En Dropout Ra (nm) (dB) (dB) Velocity (pcs / min) ─────────────────────────── ───────── Comparative Example 1 × 3.1 -2.7 -4.9 48 68 Comparative Example 2 × 2.9 -2.3 -5.4 51 65 Comparative Example 3 △ 3.6 -1.6 -3.9 48 51 Comparative Example 4 × 3.2 -2.9- 4.6 48 55 Comparative Example 5 △ 4.2 -2.9 -2.8 48 32 Comparative Example 6 × 5.9 -3.1 -5.7 41 94 Comparative Example 7 × 5.1 -3.9 -6.1 62 78 Comparative Example 8 △ 4.1 -2.9 -6.2 58 52 Comparative Example 9 × 5.1 -3.1 -5.1 46 39 Comparative Example 10 × 5.2 -3.0 -5.0 46 71 ─────────────────────────────── ─────

As shown in Table 3 and FIGS. 1 to 5, a silicone-based leveling agent was added to only the upper layer magnetic coating material in an amount of 0.05 to 1 part by weight in terms of a pure content based on the weight of the coating material. The magnetic tapes of Examples 1 to 12 have good surface properties, good electromagnetic conversion characteristics and RF envelopes, and have sufficiently suppressed dropout.

On the other hand, in the magnetic tapes of Comparative Examples 1 to 9 in which the amount of the silicone-based leveling agent added to the magnetic paint for the upper layer did not satisfy the predetermined condition, the surface of the upper magnetic layer was rough. For this reason, the electromagnetic conversion characteristics are insufficient, and dropouts occur frequently. Also, R
The shape of the F envelope is also poor.

From the above, it was found that a silicone-based leveling agent was added to the magnetic paint for the upper layer in an amount of 0.0
It has been found that the addition of 5 parts by weight or more and 1 part by weight or less is effective for producing a multilayer coating type magnetic recording medium having the above-mentioned properties and producing the same. In particular, when the addition amount of the silicone-based leveling agent is 0.5 parts by weight or more in terms of the pure content, the addition effect on the surface roughness Ra is improved (see FIG. 1).

Further, from Examples 13 to 15, magnetic tapes obtained by adding a predetermined amount of a silicone-based leveling agent to each of the magnetic paint for the upper layer and the non-magnetic paint for the lower layer also showed good magnetic recording characteristics. It turned out to be a medium.

Further, from Comparative Example 10, even when a silicone-based lubricant was included in the magnetic paint for the upper layer, the magnetic tape to which no silicone-based leveling agent was added had a rough surface of the upper magnetic layer, For this reason, the electromagnetic conversion characteristics are insufficient, and dropouts occur frequently. Also,
The shape of the RF envelope was also found to be poor.

Although the present invention has been described with reference to the embodiments, the embodiments can be further modified based on the technical idea of the present invention.

For example, in this embodiment, a magnetic tape (8 mm video tape) is used as the magnetic recording medium according to the present invention.
Was evaluated, but it is of course possible to use it for a disk medium such as FD (floppy disk, flexible disk), and also applicable to a medium for digital recording and reproduction such as a digital video tape (DVC) for home use. is there.

[0143]

According to the magnetic recording medium of the present invention, a non-magnetic layer made of a non-magnetic powder and a binder is used as a lower layer, and a magnetic layer (upper layer) made of a magnetic powder and a binder is provided on the lower layer. At least 0.05 parts by weight or more and 1 part by weight or less of the silicone leveling agent in the magnetic layer (provided that the coating material for forming the magnetic layer is 100 parts by weight, In particular, even when the thickness of the magnetic layer is very small, such as 0.3 μm or less, the magnetic layer has good surface properties even if the magnetic layer has a very small thickness of 0.3 μm or less. In addition to having excellent electromagnetic conversion characteristics, the shape of the RF envelope is also good, and further, dropout is suppressed,
A magnetic recording medium having excellent running durability can be obtained.

According to the production method of the present invention, a step of preparing a non-magnetic paint by dispersing a non-magnetic powder and a binder together with a solvent, and applying the prepared non-magnetic paint to a non-magnetic support Forming a non-magnetic layer (lower layer), preparing a magnetic paint by dispersing a magnetic powder and a binder together with a solvent, and disposing the prepared magnetic paint while the non-magnetic layer is in a wet state. Forming a magnetic layer (upper layer) by coating on the non-magnetic layer (so-called wet-on-wet coating). Therefore, even if the thickness of the magnetic layer is reduced to 0.3 μm or less, for example, The surface of the magnetic paint is coated with a leveling agent in addition to being dried at the same time as the non-magnetic paint, even if the amount of the magnetic paint is reduced, so that the surface due to local evaporation of the solvent Shadow on sex The magnetic layer having good surface properties can be formed by eliminating the problem, and the magnetic coating film is sufficiently flattened (leveled) and dried, and the adhesion between the magnetic layer and the non-magnetic layer is improved. And good running durability can be obtained.

That is, at least 0.05 part by weight or more and 1 part by weight or less of a silicone-based leveling agent per 100 parts by weight of the magnetic paint in the non-magnetic paint and the magnetic paint (silicone-based leveling). Even when such a small amount is added, the silicone-based leveling agent is effectively unevenly distributed on the surface of the coating film (especially a magnetic coating film), and the solvent is partially localized. Moderate volatilization, suppress the non-uniformity of the coating film after drying, can form the magnetic layer with good surface properties, have excellent electromagnetic conversion characteristics, and the shape of the RF envelope In addition, it is possible to manufacture a magnetic recording medium in which dropout is suppressed and running durability is excellent.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in surface roughness Ra depending on the amount of a silicone-based leveling agent added.

FIG. 2 is a graph showing a change in CS / N (chroma-S / N).

FIG. 3 is a graph showing a change in LS / N (Lumi-S / N).

FIG. 4 is a graph showing a change in an RF envelope.

FIG. 5 is a graph showing a change in dropout.

FIG. 6 is a schematic view showing a coating film forming system for forming a lower non-magnetic layer and an upper magnetic layer by a wet-on-wet coating method applicable to the manufacturing method of the present invention.

FIG. 7A is a schematic cross-sectional view of an example of a usable coating apparatus, and FIG. 7B is a schematic cross-sectional view of an example of another coating apparatus.
It is a schematic sectional drawing (C) of an example of the same other coating apparatus.

FIG. 8 is a schematic diagram of a main part showing a state in which a film made of a silicone-based leveling agent is formed on the surface of the upper magnetic layer based on the manufacturing method of the present invention.

FIG. 9 is a schematic sectional view of an example of the magnetic recording medium of the present invention.

[Explanation of symbols]

1 ... magnetic recording medium, 2, 24 ... nonmagnetic layer (lower layer), 3,
25: magnetic layer (upper layer), 4: back coat layer, 5: coating, 6: interface, 7: surface, 11: non-magnetic support, 12: take-up roll, 13: supply roll, 14: coating device, Fifteen
... Orienting magnet, 16 ... Dryer, 17 ... Calendar device,
18, 19, 26, 31 ... Extrusion coater, 20, 2
2, 28, 30 ... slit parts, 21, 23, 27, 29
… Paint pool

Claims (7)

[Claims] 1. A magnetic recording medium comprising a non-magnetic layer made of a non-magnetic powder and a binder as a lower layer, and a magnetic layer made of a magnetic powder and a binder provided on the lower layer. 0.05 leveling agent
Ratio of not less than 1 part by weight and not more than 1 part by weight (provided that the paint for forming the magnetic layer is 100 parts by weight)
A magnetic recording medium characterized by containing: 2. The magnetic recording medium according to claim 1, wherein said magnetic layer has a thickness of 0.3 μm or less. 3. The magnetic recording medium according to claim 1, wherein the silicone leveling agent is a modified polysiloxane. 4. A step of preparing a non-magnetic coating by dispersing a non-magnetic powder and a binder together with a solvent, and a step of applying the prepared non-magnetic coating to a non-magnetic support to form a non-magnetic layer. And preparing a magnetic paint by dispersing a magnetic powder and a binder together with a solvent, and applying the prepared magnetic paint onto the non-magnetic layer while the non-magnetic layer is in a wet state to form a magnetic layer. Forming a silicone leveling agent in a proportion of at least 0.05 part by weight and not more than 1 part by weight per 100 parts by weight of the magnetic paint in at least the magnetic paint out of the non-magnetic paint and the magnetic paint. A method for producing a magnetic recording medium. 5. The method according to claim 4, wherein the magnetic layer and the non-magnetic layer are formed using an extrusion coater. 6. The method according to claim 4, wherein said magnetic layer has a thickness of 0.3 μm or less. 7. The method according to claim 4, wherein the silicone-based leveling agent is a modified polysiloxane.