JPH0628661A - Nonmagnetic base with masking layer for magnetic recording medium and magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To provide the recording medium having excellent electromagnetic conversion characteristic without increasing the cost thereof by forming a masking layer having specific surface roughness at a prescribed thickness on a nonmagnetic base having the specific surface roughness. CONSTITUTION:A bass film as the nonmagnetic base 1 has 0.035 to 0.065mum surface roughness SRa. The masking layer 4 consisting of a binder dispersing a carbon black having 10 to 100mum grain sizes in it and having 0.035mum or less surface roughness SRa and 1.0 to 4.0mum thickness is formed thereon. A magnetic coating material is applied on the surface of the masking layer 4 and the coating is dried and is subjected to a calender treatment, by that, a magnetic layer 2 is formed. The increase in the cost is averted by using the nonmagnetic base which is not so strict in the SRa in such a manner. In addition, the surface characteristic is improved by the masking layer. The medium which is decreased in drop-outs and has the excellent electromagnetic conversion characteristics is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-magnetic support with a masking layer for a magnetic recording medium such as a magnetic tape and a magnetic disk, a magnetic recording medium therefor and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, for example, in a magnetic tape, the surface properties of a magnetic layer affect performances such as dropout, electromagnetic conversion characteristics, and running property. Therefore, various measures have been taken for the control. .

One of the methods is to control the surface roughness of the base film, which is a non-magnetic support, but this is usually performed by the manufacturer of the base film depending on the film forming conditions.

In this case, if the surface roughness of the base film is improved, good surface properties can be obtained even if the magnetic layer formed thereon is thinned or densified.
However, it enhances the surface property of the base film (that is, SR
If a is reduced), the manufacturing cost of the base film will naturally increase.

[0005]

DISCLOSURE OF THE INVENTION The present invention realizes a desired surface property without increasing the manufacturing cost of the base film as described above, and can improve the performance such as dropout. It is an object of the present invention to provide a non-magnetic support with a masking layer, a magnetic recording medium, and a method for producing the same.

[0006]

[Means for Solving the Problems] That is, the first invention of the present application is such that a surface roughness SRa is 0.035 μm or less and a thickness is 0.035 μm or less on a non-magnetic support having a surface roughness SRa of 0.035 to 0.065 μm.
A masking layer having a thickness of 1.0 to 4.0 μm is provided,
The present invention relates to a non-magnetic support with a masking layer for a magnetic recording medium.

Another aspect of the present invention is a magnetic recording medium in which a magnetic layer is formed on a non-magnetic support via a masking layer, and the surface roughness SRa of the non-magnetic support is
The masking layer has a surface roughness SRa of 0.035 μm or less and a thickness of 1.0 to 4.0 μm.

In the present invention, the masking layer is preferably composed of a binder in which carbon black having a particle size of 10 to 100 mμ is dispersed.

The present invention also provides a method for producing a magnetic recording medium, in which the masking layer and the magnetic layer are formed on a non-magnetic support by simultaneous wet multi-layer coating.

According to the present invention, the surface roughness (SRa) of the nonmagnetic support is not so severe 0.035 to 0.065 μm.
However, since the support of such surface roughness is one rank lower than that of the regular class,
The manufacturing cost does not rise, but rather can be reduced.

Even on such a non-magnetic support, a masking layer having a surface roughness SRa of 0.035 μm or less is formed on the support.
Since it is formed with a thickness of 1.0 to 4.0 μm, the surface of this non-magnetic support with a masking layer can be made smooth and it can be used as a support one grade above.

In this case, even if there are projections called fisheyes on the non-magnetic support, they can be sufficiently masked by the masking layer having the above-mentioned thickness. No adverse effect occurs on the masking layer surface.

As described above, a non-magnetic support having a smooth surface property can be provided at low cost, and the surface property of the magnetic layer formed on the masking layer can be improved, resulting in less dropout and electromagnetic conversion. It is possible to provide a medium having excellent characteristics.

FIG. 1 shows an example (magnetic tape for video) of the magnetic recording medium of the present invention. That is, a magnetic layer 2 containing magnetic powder, a binder, etc. is provided on one surface of the non-magnetic support 1 via a masking layer 4 containing carbon black. Further, the other surface may have a back coat layer 3 mainly composed of a non-magnetic powder and a binder as indicated by a chain line.

The base film as the non-magnetic support 1 has SRa = 0.035 to 0.065 μm (preferably 0.04 to 0.06 μm).
Although it has a surface roughness of m), if SRa is less than 0.035 μm, it becomes smooth and the manufacturing cost rises. If it exceeds 0.065 μm, the surface becomes rough and the masking effect of the masking layer is increased. Get scarce.

The masking layer 4 has SRa of 0.035 μm.
m or less and 1.0 to 4.0 μm (preferably 1.
It has a specific thickness of 0-3.0 μm) but SRa of 0.
If it exceeds 035 μm, the surface properties will deteriorate and the thickness will be 1.0
If it is less than μm, it is too thin and has no masking effect.
If it exceeds μm, it is too thick, which is disadvantageous for thinning the medium.

To form a magnetic layer in the magnetic recording medium of the present invention, for example, magnetic powder is dispersed in a binder, and ethers, ketones, aromatic hydrocarbons, and aliphatic carbons are used depending on the kind of the binder. A magnetic paint is prepared by kneading with an organic solvent selected from hydrogen, chlorinated hydrocarbons and the like, and the magnetic paint is applied to the surface of the non-magnetic support, dried and calendered.

As the magnetic powder used in the present invention, any conventionally known magnetic powder can be used. It is possible to use oxide magnetic powders, which include
For example, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-deposited γ-Fe
₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-deposited Fe ₃ O ₄ , CrO _{2 and the} like can be mentioned. Further, hexagonal ferrite such as barium ferrite, iron carbide such as Fe ₅ C ₂ and iron nitride can also be used.

The usable magnetic metal powders are
For example, Fe, Co, Ni, Fe-Co, Fe-Ni, Fe-Co-Ni, Co
-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn-Al,
Fe-Co-V and the like can be mentioned, and further, metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added for the purpose of improving these various characteristics.

As the above-mentioned binder, a modified or unmodified vinyl chloride resin, polyurethane resin or polyester resin can be used or mixed, and further, a fibrin resin, a phenoxy resin or a heat having a specific usage method. You may use together plastic resin, thermosetting resin, reaction type resin, electron beam irradiation hardening type resin, etc. The group introduced for the above modification can improve the dispersibility of the magnetic powder --SO.
₃ M, -OSO ₃ M, -COOM, -PO (OM ') _{2 and the} like (M
Is an alkali metal atom such as Na, M'is the same alkali metal atom or an alkyl group).

As the usable fibrous resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

Further, it is preferable to add a curing agent to such a binder in order to further improve the durability. As this curing agent, a polyfunctional isocyanate can be used, and particularly tolylene diisocyanate (T
The DI) system is preferred. The addition amount of the curing agent is preferably 5 to 30% by weight based on the total amount of the binder.

In the magnetic recording medium of the present invention,
In addition to the above binder and magnetic powder, a dispersant such as lecithin, an abrasive such as alumina, a lubricant such as stearic acid, an antistatic agent such as carbon black, and a rust preventive may be added, if necessary. Good. As the dispersant, the abrasive, the lubricant, the antistatic agent and the rust preventive, any of conventionally known materials can be used, and there is no limitation.

The masking layer formed under the magnetic layer includes
The same binder as described above can be used, and carbon black, γ-Fe ₂ O ₃ or the like can be dispersed in the binder to adjust the surface roughness. Examples of the binder that can be used include the above-mentioned binders, but a combination of a vinyl chloride copolymer and a urethane resin, a combination of nitrocellulose and a urethane resin, and the like are preferable.

The carbon black to be dispersed in the masking layer preferably has a particle size of 10 to 100 mμ. If the particle size is too small, poor dispersion will occur, and if it is too large, the surface properties of the masking layer will tend to deteriorate.

Examples of carbon blacks that can be used include conductive carbon blacks such as Conductex 900 and light-shielding carbon blacks such as Raven 200.

The non-magnetic support usable in the present invention includes polyethylene terephthalate and polyethylene-
Polyesters such as 2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate,
Examples include plastics such as polyamide and polycarbonate. Further, metals such as Cu, Al and Zn, glass, boron nitride, ceramics such as Si carbide and the like can also be used.

Further, on the surface of the non-magnetic support opposite to the magnetic layer, a non-magnetic powder (eg silica, carbon black) and a binder (similar to those mentioned above) are used to improve the running property of the medium. Back coat layer consisting of
It can be provided in a thickness of 0.4 to 0.8 μm.

When a masking layer and a magnetic layer are formed on a non-magnetic support, a method of performing a coating and drying step one layer at a time (so-called wet-on-dry coating method) and a masking layer which is not dried but in a wet state are used. There is a method of coating a magnetic layer on top of it (so-called wet-on-wet coating method = wet multi-layer coating method).

In the production of the magnetic recording medium of the present invention, a non-magnetic support having a dry masking layer may be first produced by the wet-on-dry coating method, and the magnetic layer may be coated thereon. -It is preferable to perform simultaneous wet multi-layer coating by an on-wet multi-layer coating method.

FIG. 2 shows an example of a preferred manufacturing method according to the present invention. In this manufacturing method, for example, in manufacturing the medium shown in FIG. 1, first, the film-shaped support 1 fed from the supply roll is processed by the extrusion coater 10 of the extrusion method to form the masking layer 4 described above.
And the coating materials 4'and 2'for the magnetic layer 2 are simultaneously coated in multiple layers.

The extrusion coater 10 is provided with liquid reservoirs 13 and 14, and the coating materials 2'and 4'are simultaneously overlaid in a wet-on-wet system. In such wet-on-wet simultaneous wet multi-layer coating, since the lower masking layer is in a wet state and the upper magnetic layer is applied, the surface of the lower layer (that is, the boundary surface between the upper layer) and the upper layer are smooth. In some cases, the surface property is improved and the calendering process may be omitted, and the adhesiveness between the upper and lower layers is also improved.

As a result, the performance required as a magnetic recording medium that requires high output and low noise for high density recording is satisfied, and high durability performance is required. Also, the film peeling is eliminated, the film strength is improved, and the durability is sufficient. Also, dropout can be reduced and reliability is improved.

On the other hand, in the case of the wet-on-dry method, it is necessary to select, as the underlying masking layer, one having sufficient solvent resistance to the solvent used for the paint of the upper magnetic layer.

The components of both layers are mixed with a constant thickness except that a clear boundary is substantially present between the upper and lower layers formed by the wet-on-wet multi-layer coating method. Although a boundary region may exist, the upper or lower layer excluding such a boundary region is used as the above magnetic layer or masking layer. Either case is included in the scope of the present invention.

After the above-mentioned multi-layer coating, it is introduced into a drier, and if necessary, it is led to a calendar device and wound on a winding roll. The magnetic film thus obtained is slit to, for example, 1/2 inch to prepare a magnetic tape, which is housed in a cassette to manufacture a tape cassette.

[0037]

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

Example 1 The following carbon black dispersion paint was prepared as a paint for the masking layer.

Carbon black (average particle size 20 mμ) 100 parts by weight Binder: Nitrocellulose (Celnova BTH1 / 2 manufactured by Asahi Kasei Corporation) 50 parts by weight Polyester polyurethane (N-2304 manufactured by Nippon Polyurethane Co., Ltd.) 50 parts by weight Solvent: Methyl ethyl ketone 230 Parts by weight Toluene 230 parts by weight

The above composition was well dispersed by a three-roll mill and a ball mill and then filtered to obtain a coating material for a masking layer. This was applied to a polyethylene terephthalate base having a surface roughness SRa of 0.06 μm so as to have a specified thickness.

The results are shown in FIG. 3. When SRa was measured while changing the thickness of the masking layer, it was found that SRa tends to decrease depending on the thickness.

SRa was measured as follows (the same applies hereinafter). SRa: Measured with a surface roughness meter [SE-30H] manufactured by Kosaka Laboratory. The conditions are magnification 50,000 times, measurement length 2mm, cutoff value
It was performed at 0.08 mm.

Example 2 Based on the results of Example 1, a magnetic coating composition for VHS having the following composition was prepared in the upper layer, and the above masking layer was formed in the lower layer while changing the thickness. Multiple layers were coated by the simultaneous extrusion method (however, the magnetic layer thickness was 1μ
m).

<Magnetic paint> Magnetic powder: Co-γ-Fe ₂ O ₃ (specific surface area BET value = 45 m ² / g) 100 parts by weight Binder: Polyester polyurethane resin (N-2304 manufactured by Nippon Polyurethane Co., Ltd.) 10 parts by weight Chloride Vinyl-based copolymer (VACH manufactured by UCC) 10 parts by weight Abrasive: α-alumina 4 parts by weight Carbon (average particle size 25 nm) 5 parts by weight Solvent: methyl ethyl ketone 120 parts by weight Cyclohexanone 120 parts by weight

Then, after the steps of calendering, curing and slitting, they were incorporated into a cassette for T-120 and recorded and reproduced by a Sony VTR, and the dropout and electromagnetic conversion characteristics (RF output) at that time were as follows. Was measured.
The results are shown in Fig. 4.

Dropout: A dropout having a video head-up output attenuation of 12 dB during reproduction and a duration of 5 μ _SEC or more was measured by a dropout counter for 10 minutes and calculated as an average value per minute.

RF output: An RF output at 6 MHz was measured using a DVR-1000 deck manufactured by Sony Corporation.

From the results shown in FIGS. 3 and 4, the following is clear. The SRa = 0.06 μm base film without masking layer has 50 or more dropouts, resulting in poor image quality. In addition, the RF-output is also a bad Ref ratio of -3 dB.

On the other hand, according to the present invention, the thickness
It was found that those having a masking layer of 1.0 to 4.0 μm (particularly 1 to 3 μm) were within the practical range for both dropout and RF output.

[0050]

INDUSTRIAL APPLICABILITY As described above, the present invention has a surface roughness (SRa) of 0.035 as a non-magnetic support.
Since it uses ~ 0.065 μm, its manufacturing cost does not increase and can be reduced. And even such a non-magnetic support has a surface roughness SRa of 0.035 μm.
Since the following masking layer is formed with a thickness of 1.0 to 4.0 μm, the surface of the non-magnetic support with the masking layer can be made smooth and it can be used as an upgraded support.

In this case, even if there are projections on the non-magnetic support, they can be sufficiently masked by the masking layer having the above-mentioned thickness. It never happens.

As described above, a non-magnetic support having a smooth surface property can be provided at low cost, the surface property of the magnetic layer formed on the masking layer can be improved, and dropouts can be reduced, resulting in electromagnetic conversion. It is possible to provide a medium having excellent characteristics.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one structural example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view showing a coater portion during simultaneous wet multi-layer coating.

FIG. 3 is a graph showing changes in surface roughness depending on the thickness of a masking layer.

FIG. 4 is a graph showing changes in dropout and reproduction output depending on the thickness of a masking layer.

[Explanation of symbols]

 1 ... Non-magnetic support 2 ... Magnetic layer 3 ... Back coat layer 4 ... Masking layer

Claims (5)

[Claims] 1. A non-magnetic support having a surface roughness SRa of 0.035 to 0.065 μm and a surface roughness SRa of 0.035 μm or less,
A non-magnetic support with a masking layer for a magnetic recording medium, which is provided with a masking layer having a thickness of 1.0 to 4.0 μm. 2. The non-magnetic support according to claim 1, wherein the masking layer comprises a binder in which carbon black having a particle size of 10 to 100 μm is dispersed. 3. A magnetic recording medium in which a magnetic layer is formed on a non-magnetic support through a masking layer, wherein the non-magnetic support has a surface roughness SRa of 0.035 to 0.065 μm. A magnetic recording medium having a surface roughness SRa of 0.035 μm or less and a thickness of 1.0 to 4.0 μm. 4. The magnetic recording medium according to claim 3, wherein the masking layer comprises a binder in which carbon black having a particle diameter of 10 to 100 μm is dispersed. 5. A method for producing a magnetic recording medium, wherein the masking layer and the magnetic layer according to claim 3 or 4 are formed on the non-magnetic support according to claim 3 by simultaneous wet multi-layer coating.