JPH10326414A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make such a magnetic recording medium compatible in electromagnetic conversion characteristics and a good traveling property, that uses a nonmagnetic base having surface roughness to some extent so that the good traveling property may be maintained even if a back-coating layer is not formed. SOLUTION: This medium is so constituted that a nonmagnetic layer formed by dispersing nonmagnetic powder into a binder and a magnetic layer formed by dispersing ferromagnetic powder into a binder are formed on the nonmagnetic base via a calender treatment stage. At this time, the gap quantity of the nonmagnetic layer before the calender treatment is 30 to 45 vol.%. In addition, the medium is so formed as to satisfy the equation 0.03<=D±2σ<0.08 when the standard deviation of the average diameter D (μm) of the gaps is defined as σ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium such as a video tape.

[0002]

2. Description of the Related Art As a coating type magnetic recording medium, a medium having a single layer structure in which a magnetic layer is formed on a nonmagnetic support, and a nonmagnetic powder between a magnetic layer and the nonmagnetic support are used as a binder. A medium having a two-layer structure further provided with a non-magnetic layer dispersed in a magnetic recording medium is known. In these magnetic recording media, more magnetic powder is filled in a magnetic layer which is a layer on which recording is performed. Is known to improve the electromagnetic conversion characteristics. It is also known that it is necessary to add a pigment such as carbon as a component for improving the electric resistance and the transmittance to the magnetic layer in order to improve the running property of the magnetic recording medium.

For this reason, in the case of a single-layer type magnetic recording medium,
The addition of a pigment such as carbon results in a decrease in the filling rate of the magnetic layer, and it has been very difficult to achieve both improvement in electromagnetic conversion characteristics and running performance. On the other hand, in the case of a two-layer type magnetic recording medium, a material capable of setting the electric resistance and transmittance of the entire magnetic recording medium to a desired range at a desired filling rate is added to the lower non-magnetic layer. As a result, the running properties of the magnetic recording medium can be ensured, and therefore, the amount of additives other than the ferromagnetic powder and the amount of additives such as pigments added to the upper magnetic layer, such as pigments, should be reduced as much as possible to increase the filling amount of the magnetic powder in the magnetic layer. Can be
It is possible to improve the electromagnetic conversion characteristics of the magnetic recording medium.

[0004] However, even if the filling rate of the ferromagnetic powder in the magnetic layer is increased, there is a problem that if the surface properties of the magnetic recording medium are poor, the electromagnetic conversion characteristics are eventually reduced.
Therefore, from the viewpoint of improving the electromagnetic conversion characteristics of the magnetic recording medium, it is desired to employ a non-magnetic support having a small number of protrusions on the surface on the magnetic layer side as the non-magnetic support of the magnetic recording medium.

[0005] By the way, the non-magnetic support widely used in VHS video tapes and the like has no difference in roughness between the surface on which the magnetic layer is coated and the surface on the opposite side, and is very smooth. . When such a non-magnetic support is used, it is possible to set the electromagnetic conversion characteristics to the expected values.However, due to the high smoothness of the non-magnetic support opposite to the coated surface, video The friction during running of the magnetic recording medium such as a tape increases, and the running durability decreases. For this reason, in order to maintain good running properties, it is usually necessary to provide a back coat layer on the surface opposite to the coating surface of the non-magnetic support, to design the friction coefficient to be small and to have an appropriate roughness. Is being done.

[0006]

In recent years, the price of video cassette tapes and the like has tended to be inexpensive. In order to reduce the production cost, it is necessary to further increase the productivity. It has been demanded that no backcoat layer be provided on the body.

By the way, in order to ensure the running property of the magnetic recording medium without providing a back coat layer on the non-magnetic support, a non-magnetic support having a certain surface roughness necessary for maintaining good running property is required. It is necessary to use a magnetic support. However, the use of a non-magnetic support having a rough surface to some extent causes a problem that the electromagnetic conversion characteristics of the magnetic recording medium are deteriorated.

The present invention has been made to solve the above-mentioned problems of the prior art, and has a certain surface roughness so as to maintain a good running property without forming a back coat layer. It is an object of the present invention to provide a magnetic recording medium using a non-magnetic support having excellent running properties and electromagnetic conversion characteristics.

[0009]

Means for Solving the Problems The present inventors provide a nonmagnetic layer in which a nonmagnetic powder is dispersed in a binder between a magnetic layer and a nonmagnetic support, and the nonmagnetic layer before calendering is provided. It has been found that the above object can be achieved by keeping the porosity and the size of the voids in specific ranges, and have completed the present invention.

That is, the present invention relates to a method of calendering a nonmagnetic layer in which nonmagnetic powder is dispersed in a binder and a magnetic layer in which ferromagnetic powder is dispersed in a binder on a nonmagnetic support. In the magnetic recording medium formed through the steps, the void amount of the nonmagnetic layer before the calendering treatment is 30 to 45 vol.
%, And the average diameter D (μm) of the voids is represented by the standard deviation σ.

[0011]

(3) Provided is a magnetic recording medium characterized by satisfying 0.03 ≦ D ± 2σ <0.08 (1).

In this case, the surface roughness SRa (nm) and SRz (nm) of the surface of the non-magnetic support on which the non-magnetic layer is not formed according to JIS B0601-1982 are expressed by the following equations (2) and (z), respectively. 3)

[0013]

It is preferable that the following condition is satisfied: 10 ≦ SRa ≦ 15 (2) 200 ≦ SRz ≦ 450 (3) This makes it possible to maintain good running properties of the magnetic recording medium without providing a backcoat layer on the nonmagnetic support.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the magnetic recording medium of the present invention, a non-magnetic layer formed by dispersing a non-magnetic powder in a binder and a magnetic layer formed by dispersing a ferromagnetic powder in a binder are formed on a non-magnetic support. This is a magnetic recording medium formed through a calendering process. In the present invention, when the amount of voids in the nonmagnetic layer before calendering is 30 to 45 vol%, and the average diameter D (μm) of the voids is standard deviation σ, equation (1) is used.

[0016]

## EQU5 ## It is characterized by satisfying 0.03 ≦ D ± 2σ <0.08 (1).

Regarding the significance of such features of the present invention,
This will be described below.

Generally, at the stage of manufacturing a magnetic recording medium, there is a calendering step for mirror-finishing the surface of the magnetic recording medium. Also, in order to improve the electromagnetic conversion characteristics of a magnetic recording medium such as a video tape, it is necessary to increase the filling rate of the ferromagnetic powder in the magnetic layer at the stage of applying the magnetic paint.
A magnetic layer containing a ferromagnetic powder at a high filling factor has a property that the amount of voids in the layer is small.

Therefore, when the magnetic layer containing the ferromagnetic powder at a high filling factor is subjected to the calendering treatment, the magnetic recording medium is rough enough to provide good running properties without providing a back coat layer. There is a problem that the protrusions on the surface of the non-magnetic support having surface properties cannot be alleviated, and as a result, the surface of the magnetic layer becomes rough, and the electromagnetic conversion characteristics deteriorate.

In order to solve this problem, in the present invention, a non-magnetic layer formed by dispersing a non-magnetic powder in a binder is provided between a non-magnetic support and a magnetic layer. The amount of voids in the magnetic layer is set to a value larger than the amount of voids in the magnetic layer having a small amount of void (that is, highly dispersed), that is, 30 to 45 v
ol%, and the average diameter of the voids is also set in the range of Expression (1). When such a non-magnetic layer is subjected to a calendering treatment, the voids absorb the protrusions on the non-magnetic support, thereby improving the surface properties of the magnetic layer and, accordingly, the electromagnetic conversion characteristics.

It is preferable to promote the collapse of the magnetic layer during the calendering process in order to improve the surface properties of the magnetic layer. For this purpose, the non-magnetic layer needs to be hardened to some extent. In other words, the non-magnetic layer is crushed in the first stage of the calendering process, thereby absorbing the protrusions of the non-magnetic support, and the non-magnetic layer itself becomes smooth and the layer becomes hard, so that the non-magnetic layer is in the middle of the calendering process. Can function as a support for the magnetic layer. Thereby, the collapse of the magnetic layer is promoted, and the surface property is improved.

When the non-magnetic layer is softer than the magnetic layer, the magnetic layer is insufficiently crushed, resulting in deterioration of the surface properties of the magnetic recording medium. Therefore, the hardness of the nonmagnetic layer is preferably equal to or higher than that of the magnetic layer around the calendering temperature. In this case, in order to increase the hardness of the nonmagnetic layer relative to the magnetic layer, for example, the ratio of the resin having a high glass transition point may be higher than that of the magnetic layer.

Next, a method for realizing the above-mentioned predetermined porosity and the average diameter of the voids in the non-magnetic layer in the present invention will be described.

In a general manufacturing process of a magnetic recording medium, when preparing a non-magnetic coating material for forming a non-magnetic layer, a non-magnetic powder or an aggregate of pigments (secondary particles) is used as primary particles. A dispersing device such as a sand mill is used to disperse the agglomerates such as non-magnetic powder with a device having a high shearing force such as a continuous kneader to disperse the particles, and further to form primary particles.

On the other hand, when preparing a non-magnetic paint in the present invention, a process such as kneading that exerts a high shear force is omitted, and the paint is dispersed by a device such as a sand mill.
Alternatively, when a process such as kneading is performed, the predetermined porosity and the average diameter of the voids described above can be realized in the nonmagnetic layer by shortening the operation time of the dispersing device such as a sand mill. Also, by adjusting the amount of the binder of the non-magnetic paint, it is possible to adjust the void amount and the void diameter of the non-magnetic layer, but weakens the bonding force between the non-magnetic layer and the non-magnetic support, It should be noted that running durability tends to decrease.

In the present invention, the calendering temperature is usually about 100 ° C., and the elastic modulus of the magnetic layer and the non-magnetic layer around this temperature is 900 to 1200 kg / mm.
^{About 2} is desirable. If the elastic modulus is less than this, it becomes too soft when taped, the contact surface of the head etc. increases, friction rises, powder fall etc. occurs, and there is a concern that running durability decreases, and if it exceeds, it becomes hard. There is a concern that the stress of the head or the like may not be alleviated, and powder running off the tape surface may occur due to repeated running, thereby lowering running durability.

In a preferred embodiment of the magnetic recording medium of the present invention, the surface roughness SRa (nm) and SRz (nm) of the surface of the non-magnetic support on which the non-magnetic layer is not formed.
Regarding the above, there may be mentioned an embodiment in which the former is 10 nm or more and 15 nm or less and the latter is 200 nm or more and 450 nm or less. A magnetic recording medium having such a surface roughness can achieve good running properties without providing a back coat layer.

As described above, the magnetic recording medium of the present invention has a configuration other than setting the porosity and the pore diameter of the nonmagnetic layer provided between the nonmagnetic support and the magnetic layer to a predetermined range. Elements, ie, non-magnetic support, ferromagnetic powder mixed in magnetic layer, binder, dispersant used as needed, abrasive, antistatic agent, rust inhibitor, or coating type magnetic recording medium The solvent used for preparing the magnetic paint in the above can be a conventionally known material.

For example, as the non-magnetic support, those generally used as a non-magnetic support for a magnetic recording medium can be used, and polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyethylene, polypropylene and the like can be used. Polyolefins, cellulose triacetate, cellulose diacetate, cellulose derivatives such as cellulose acetate butyrate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, polycarbonate, polyimide, polyamide imide, other plastics, metals such as aluminum and copper, Examples thereof include materials obtained by processing materials such as aluminum alloys, light alloys such as titanium alloys, ceramics, single crystal silicon, and the like into a film shape, a sheet shape, a disk shape, and the like by an ordinary method.

As the ferromagnetic powder used for the magnetic layer, γ
-FeO _x (x = 1.33 to 1.5), Co-modified γ-Fe
O _x (x = 1.33-1.5), Fe or Ni or Co
Known ferromagnetic materials such as ferromagnetic alloys containing barium as a main component (75% or more), barium ferrite, and strontium ferrite. Further, these ferromagnetic materials further include Al, Si, S, Sc, Ti, V, Cr, C
u, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te,
Ba, Ni, Ta, W, Re, Au, Hg, Pb, B
It may contain atoms such as i, La, Ce, P, Mn, Zn, Co, Sr, and B.

As the binder in the magnetic layer or the non-magnetic layer, any known materials can be used. For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-
Vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, acrylate-vinylidene chloride copolymer, acrylate-acrylonitrile Copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer,
Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde Resins, polyvinyl acetal resins, and mixtures thereof can be used. Among these, it is desirable to use a polyurethane resin, a polyester resin, an acrylonitrile-butadiene copolymer or the like capable of imparting flexibility to the magnetic layer in combination with a cellulose derivative, a phenol resin, an epoxy resin or the like capable of imparting rigidity.

Further, it is preferable to improve running durability by crosslinking the above binder with a crosslinking agent such as an isocyanate compound. Further, a binder modified by introducing a polar group may be used.

The lubricant usable in the present invention includes silicone oil, fatty acid-modified silicone, fluorine-containing silicone or other fluorine-based lubricant, polyolefin, polyglycol, alkyl phosphate and its metal salt, polyphenyl ether, Fluorinated alkyl ethers, linear or branched saturated or unsaturated alcohols having 12 to 24 carbon atoms, higher saturated or unsaturated fatty acids having 12 to 24 carbon atoms and esters thereof, amine salts of alkyl carboxylic acids and fluorinated alkyl carboxylic acids Lubricants such as acid amine salts can be used. Here, specific examples of higher saturated or unsaturated fatty acids having 12 to 24 carbon atoms and esters thereof include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid and elaidin. Acid, hebenic acid, linoleic acid,
Linoleic acid, octyl stearate, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, heptyl stearate and the like can be mentioned. These lubricants may be used alone or in combination of two or more.

As the abrasive which can be used in the present invention, known materials having a Mohs' hardness of 6 or more can be used alone or in combination. Such materials include α-alumina, β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, silica, garnet, garnet, silicon nitride, boron nitride, Molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, and the like can be given.

The average particle size of these abrasives is 0.01 to 2
Although μm is preferred, abrasives having different particle sizes may be combined as needed, or a single abrasive may be used with a broad particle size distribution.

The dispersants usable in the present invention include metal soaps comprising fatty acids having 5 to 25 carbon atoms or alkali metal salts or alkaline earth metal salts thereof, fatty acid esters, fatty acid amides, amines, and quaternary ammonium salts. Well-known dispersants such as phosphoric acid esters and boric acid esters can be used.

As the antistatic agent usable in the present invention, known antistatic agents such as natural surfactants, nonionic surfactants and cationic surfactants can be used in addition to carbon black.

The magnetic recording medium of the present invention is prepared by dispersing a ferromagnetic powder, a binder and various additives, if necessary, in a solvent to prepare a magnetic coating material. A non-magnetic paint is prepared by dispersing the agent and various additives added as necessary in a solvent, and the paint is applied to one surface of the non-magnetic support in the order of the non-magnetic paint and the magnetic paint. It can be manufactured by drying.

Here, as a solvent for preparing the magnetic paint or the non-magnetic paint, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethyl acetate Ester solvents such as monoethyl ether; glycol ether solvents such as glycol monoethyl ether and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and ethylene Chlorine-containing solvents such as chlorohydrin and dichlorobenzene are exemplified. In addition, other conventionally known organic solvents can be used.

When a ferromagnetic powder or a non-magnetic powder is dispersed in these solvents, for example, a roll mill, a ball mill, a sand mill, a tron mill, a high-speed stone mill, a basket mill, a disper, a homomixer, a kneader, a continuous kneader, an extruder, It can be performed using a homogenizer, an ultrasonic disperser, or the like.

When preparing a magnetic paint or a non-magnetic paint, the ferromagnetic powder or the non-magnetic powder and other additives may be separately dispersed and then mixed.

When the magnetic paint or the non-magnetic paint is applied to the non-magnetic support, it may be applied directly on the non-magnetic support. Alternatively, it is preferable to perform a pretreatment such as a corona discharge treatment or an electron beam irradiation treatment on the surface of the nonmagnetic support from the viewpoint of improving the adhesion of the magnetic layer.

Examples of the method of applying the magnetic paint include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, gravure coat, transfer roll coat, and cast coat. Other methods can also be used, and a non-magnetic layer and a magnetic layer may be simultaneously coated by extrusion coating.

[0044]

The present invention will be described below in more detail with reference to examples.

Examples 1 to 4 and Comparative Examples 1 to 3 A coating material for a magnetic layer and a coating material for a nonmagnetic layer for forming an upper magnetic layer and a lower nonmagnetic layer were prepared as described below.

The coating material for the magnetic layer was prepared by kneading the composition shown in Table 1 except for 4 parts of polyisocyanate and 1 part of myristic acid with a continuous kneader and then dispersing the mixture using a sand mill. 1 part and further dispersed, and the mixture was filtered through a filter having an average diameter of 1 μm or less.

[0047]

Ingredients : parts by weight Co modified γ-Fe ₂ O ₃ (specific surface area by BET method: 35 m ² / g) 100 Nitrocellulose (NC-1 / 2H, manufactured by Asahi Kasei Corporation) 6 Vinyl chloride containing sulfonic acid potassium salt Polymer 6 (trade name: MR-110, manufactured by Zeon Corporation) Polyester polyurethane resin 4 (containing carboxylic acid, molecular weight Mn: 25000) Polyester polyurethane resin 4 (containing sodium sulfonate, molecular weight Mn: 30,000) α-Al ₂ O ₃ 3 (Mohs hardness: 9, particle size: 0.4 .mu.m, Reynolds Chemicals, Inc.) Cr ₂ 0 ₃ 5 (Mohs hardness: 8, particle size: 0.5 [mu] m, manufactured by Nippon Chemical Industrial Co., Ltd.) polyisocyanate 4 (Coronate L, Nippon polyurethane Company) myristate 1 butyl stearate 1 methyl ethyl ketone 100 toluene 60 cyclohexanone 40

The coatings A to E for the nonmagnetic layer were prepared from the compositions shown in Table 2 in the same manner as in the coating for the upper magnetic layer. However, the dispersion time of the sand mill at the time of coating preparation is shown in Table 3.
The time shown in FIG.

Among these paints, the paint A for the non-magnetic layer has a nitrocellulose and vinyl chloride copolymer content under the condition that the total amount of the binder is the same as the paint for the magnetic layer. The paint D for the non-magnetic layer is equivalent to the paint less the polyurethane resin, and the urethane resin is reduced by reducing the cellulose and the vinyl chloride copolymer under the condition that the total amount of the binder is the same as the paint for the magnetic layer. Equivalent to increased paint,
The non-magnetic layer coating material E corresponds to a coating material in which the total amount of the binder is reduced with respect to the magnetic layer coating material. The coating material for the non-magnetic layer B is the same as the coating material for the non-magnetic layer A, but without using a continuous kneader, the raw materials are mixed in a mix tank and then dispersed using a sand mill. Then, 4 parts of polyisocyanate and 1 part of myristic acid were added, and 1 μm
Corresponds to those obtained by filtration through a filter having an average diameter of. The coating composition for the non-magnetic layer C is the same as the coating composition for the non-magnetic layer A, but the processing time for dispersion by a sand mill after using the kneading of the continuous kneader is reduced, and then 4 parts of polyisocyanate is added. Add 1 part of myristic acid and add 1
This corresponds to that obtained by filtration through a filter having an average diameter of μm.

[0050]

[Table 2] Coating for nonmagnetic layer A / B / CDE component (parts by weight) Co-modified γ-Fe ₂ O ₃ 100 ← ← (specific surface area by BET method 30 m ² / g) Nitrocellulose (NC-1 / 2H, manufactured by Asahi Kasei Co., Ltd.) 7 5 5 Vinyl chloride copolymer containing potassium sulfonate 7 5 5 (trade name: MR-110, manufactured by Zeon Corporation) Polyester polyurethane resin 35 3 (containing carboxylic acid, molecular weight Mn: 25,000) polyester polyurethane resin 3 5 3 (sodium sulfonate content, molecular weight _{Mn: 30000) α-Al 2} O 3 3 ← ← ( Mohs hardness: 9, particle size: 0.4 .mu.m, Reynolds Chemicals, Inc.) Cr ₂ 0 ₃ 5 ← ← (Mohs hardness: 8, particle size: 0.5 [mu] m, Nippon Chemical Industrial Co., Ltd.) carbon black 10 ← ← (specific surface area 250 meters ² / g by BET method, produced by particle size 24 nm, Cabot Corporation) polyisocyanates Preparative 4 ← ← (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) myristic acid 1 ← ← butyl stearate 1 ← ← methylethylketone 100 ← ← toluene 60 ← ← cyclohexanone 40 ← ←

The magnetic layer paints and the non-magnetic layer paints A to E obtained as described above were simultaneously coated (wet-on) on a 15 μm thick polyethylene terephthalate film using a simultaneous multilayer coating apparatus. -Wet), followed by drying and curing, followed by calendering to obtain magnetic recording media of Examples 1 to 4 and Comparative Examples 1 to 3 having a wide width. A corresponding video tape was produced by cutting this medium to 1/2 inch width.

In Tables 3 and 4, only the non-magnetic layer was applied as a single layer at the stage of producing the video tape, and the porosity, void diameter and dynamic elastic modulus of the non-magnetic layer before calendering, and Surface roughness SRa (nm) and SRz of non-magnetic support
(Nm) shows the measurement results.

Incidentally, the porosity and the pore diameter are determined by a mercury porosimeter (PORE Sizer) manufactured by Shimadzu Corporation.
9320). That is, a video tape for measurement is put into a cell of a fixed volume, and then the internal pressure of the cell is gradually increased to inject mercury into the gap of the lower magnetic layer of the video tape, and the porosity is determined from the filling amount of mercury that has entered the gap. The void diameter was determined from the following relational expression (where P is the pressure at which mercury is injected, γ is the surface tension of mercury, and θ is the contact angle of mercury).

[0054]

[Equation 6] Void diameter =-(1 / P) 4γ cos θ

The dynamic elastic modulus was determined by using the RHEOVIBRON DDV-II-EA manufactured by Toyo Baldwin Co., and obtaining the relationship between the force and elongation when the video tape was pulled in the elastic region. (Where w is the load, S is the cross-sectional area of the video tape, l is the length of the video tape, and Δl is the elongation of the video tape.)
Further, the elastic modulus (E) was determined. Here, the dynamic elastic modulus is measured continuously by giving a tensile vibration to a video tape while heating the measurement atmosphere. Therefore, the elastic modulus at the temperature in the calendering atmosphere was determined.

The elastic modulus of the magnetic layer is 900 to 950.
kg / mm ² (measurement temperature: 105 to 115 ° C.).

[0057]

E = (W / S) × (l / Δl)

[0058]

[Table 3] Comparative Example Example 1 1 2 3 4 Type of paint for non-magnetic layer A B B C C Sand mill treatment time (hr) 5 5 4 6 4 Lower magnetic layer Porosity (vol%) 25 35 38 40 43 Average void diameter (μm) ) 0.04 0.05 0.05 0.06 0.06 (2σ) 0.015 0.018 0.02 0.015 0.017 Surface roughness of non-magnetic support SRa (nm) 10 12 12 10 10 SRz (nm) 250 360 360 300 300 300 Dynamic elastic modulus of lower magnetic layer 980- 970-980-1000-980- (kg / mm ² ) 1000 1100
1000 1150 1100

[0059]

[Table 4]

With respect to the obtained video tapes of Examples 1 to 4 and Comparative Examples 1 to 3, the electromagnetic conversion characteristics and running durability were measured as described below. Further, the surface roughness SRa (nm) and SRz (nm) of the surface of the upper magnetic layer were measured. Table 5 shows the obtained results.

RF-OUT (video output) When a video signal is recorded by using a VTR BR-S711 (manufactured by JVC), and its reproduction level is set to 0 dB using the video tape of Comparative Example 1 as a reference tape. It was expressed as a relative value.

Y / S / N (Video S / N) The S / N of the video signal is represented by a relative value when the above-mentioned reference tape is set to 0 dB.

A C-OUT (chroma output) chroma signal was recorded and reproduced, and the reproduced output level was expressed as a relative value when the above-mentioned reference tape was set to 0 dB.

C / S / N (Chroma S / N) The S / N of the chroma signal is represented by a relative value when the above-mentioned reference tape is set to 0 dB.

Running Durability (Output Attenuation) A case in which a video tape is inserted into a video tape recorder in a normal temperature environment, and the output of 50 times repetition, the output attenuation of 6 dB or more for the initial running continues for 5 minutes or more. “X”, a level having no practical problem was evaluated as “O”.

[0066]

[Table 5] RF-OUT YS / N C-OUT CS / N Surface roughness (nm) Running (dB) (dB) (dB) (dB) SRa SRz Durability comparative example 1 0 0 0 0 10.0 184 ○ Example 1 +0.3 +0.1 +0.1 +0.4 9.6 142 ○ 2 +0.5 +0.1 +0.2 +1.0 8.9 98 ○ 3 +0.5 +0.1 +0.2 +0.9 9.1 165 ○ 4 +0.4 +0.1 +0.1 +0.8 8.9 167 ○ Comparative Example 200 0 -0.1 10.5 212 × 3 +0.4 +0.1 +0.1 +0.3 9.2 153 ×

From the results shown in Table 5, it can be confirmed that the porosity and the pore diameter of the nonmagnetic layer before calendering affect the electromagnetic conversion characteristics. That is, when the porosity of the nonmagnetic layer is 30 to 45 vol% before calendering and the average void diameter is larger than 0.03 and smaller than 0.08, the electromagnetic conversion characteristics of the magnetic recording medium may be improved. Recognize.

From the results of Comparative Examples 2 and 3, when the dynamic elastic modulus of the non-magnetic layer is lower than that of the magnetic layer, the surface roughness of the upper magnetic layer becomes rough, and the running durability is lowered. It turns out that there is a tendency.

Examples 5 to 7 In order to investigate the influence of the surface roughness of the non-magnetic support, a video tape was prepared in the same manner as in Example 1 except that the non-magnetic support having the surface roughness shown in Table 6 was used. Was prepared.

[0070]

[Table 6]

The same test as in Example 1 was performed on the obtained video tapes of Examples 5 to 7. In Example 5, the nonmagnetic support had small SRa and SRz. As compared with Examples 1 and 6, the surface roughness (SRa = 6.0 nm, SRz = 72 nm) of the magnetic layer became relatively small, and the result that the running durability was lowered was obtained. Further, in the case of Example 7, since the SRa and SRz of the nonmagnetic support were large, the surface roughness of the magnetic layer (SRa = 16.2 nm, SRz =
390 nm), which resulted in a decrease in electromagnetic conversion characteristics. From these results, it can be seen that regarding the surface roughness of the nonmagnetic support, SRa is preferably in the range of 10 to 14 nm, and SRz is preferably in the range of 200 to 450 nm.

[0072]

According to the present invention, a magnetic recording medium using a non-magnetic support having a certain degree of surface roughness in order to maintain good running properties without forming a back coat layer is provided. It is possible to impart both good running properties and electromagnetic conversion characteristics.

Claims (2)

[Claims] 1. A non-magnetic layer formed by dispersing a non-magnetic powder in a binder and a magnetic layer formed by dispersing a ferromagnetic powder in a binder are formed on a non-magnetic support through a calendering process. In the obtained magnetic recording medium, when the void amount of the nonmagnetic layer before the calendering process is 30 to 45 vol%, and the average diameter D (μm) of the void is a standard deviation σ, the expression (1) A magnetic recording medium satisfying the following condition: 0.03 ≦ D ± 2σ <0.08 (1) 2. The surface roughness SRa (nm) and SRz (n) of the surface of the nonmagnetic support on which the nonmagnetic layer is not formed.
2. The magnetic recording medium according to claim 1, wherein m) satisfies the following expressions (2) and (3): 10 ≦ SRa ≦ 15 (2) 200 ≦ SRz ≦ 450 (3)