JP2003317228A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability by preventing the damaging of a magnetic layer caused by disposing a back layer on the other surface of a nonmagnetic support having a magnetic layer disposed on one surface. <P>SOLUTION: The magnetic recording medium is constructed in such a manner that a nonmagnetic layer is formed on one surface side of a nonmagnetic support, a magnetic layer is disposed on the nonmagnetic layer, and a back layer is disposed on the other surface side of the nonmagnetic support. The surface of the back layer is set to the following projection height distribution: the number of projections of 20 nm or higher to less than 40 nm is 1.2/μm<SP>2</SP>or less, the number of projections of 40 nm or higher to less than 80 nm is 0.4/μm<SP>2</SP>or less, the number of projections of 80 nm or higher to less than 100 nm is 0.2/μm<SP>2</SP>or less, and the number of projections of 100 nm or higher is none. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a magnetic tape or a magnetic disk, a magnetic coating material prepared by dispersing magnetic powder in a binder is applied to a non-magnetic support to form a magnetic layer. A so-called coating type magnetic recording medium is widely used.

In the field of information processing such as computers that handle digital data, the amount of data to be handled is increasing along with the development of information processing technology, and the importance of the data to be handled is increasing. In the field of information processing such as a computer, a recording / reproducing system capable of recording a large amount of data and enabling high-speed data transmission and a recording medium used in this system have been developed as the amount of data to be handled increases.

Data handled in the field of information processing,
As a recording / reproducing system for recording measurement data, measurement data handled in the field of measurement, and further image data,
A helical scan method in which a magnetic tape is obliquely wound around a rotating drum equipped with a rotating magnetic head and is run to record and / or reproduce data by making relative sliding contact between the magnetic head and the magnetic tape. Is used.

In the recording / reproducing system for recording / reproducing data as described above, the magnetic tape is loaded when the data is recorded or reproduced by loading the predetermined tape running path on the starting end side of the magnetic tape. There is proposed a so-called linear system that allows a fixed magnetic head to run without being wound.

A helical scan type recording / reproducing system in which data is recorded / reproduced by slidably contacting a rotating magnetic head with a rotating magnetic head, the entire capacity of a magnetic tape from a starting end to a terminating end is reduced by one tape pass. It is possible to record, and because the speed at which the magnetic tape moves on the rotating magnetic head is slower than that of a linear system, it is possible to easily stabilize the running of the magnetic tape, and stable recording and reproduction of data. Can be easily realized.

On the other hand, a recording / reproducing system adopting a linear system runs a magnetic tape against a fixed magnetic head a plurality of times in both the forward and reverse directions at a relatively high speed. Since the parts other than the recording surface are not in contact with the magnetic head, the damage to the magnetic tape and the magnetic head is less than in the helical scan system.

As a technique for increasing the recording capacity of the recording medium used in the recording / reproducing system as described above, there is a thin magnetic layer formed on the recording medium. By reducing the thickness of the magnetic layer formed on the non-magnetic support that composes the recording medium, the self-demagnetization loss during data recording and the thickness loss during data reproduction can be reduced. This is because it is possible to effectively improve the electromagnetic conversion characteristics in the recording area. As a problem caused by thinning the magnetic layer, there is a problem of spacing loss in which the gap between the recording medium and the magnetic head fluctuates due to the unevenness generated on the surface of the magnetic layer. This is a problem caused by the fact that when the magnetic layer is thinned, its surface state depends on the surface property of the non-magnetic support on which the magnetic layer is formed. If the surface is rough, the surface of the magnetic layer will also be rough, and as a result, spacing loss will occur, causing deterioration of the electromagnetic conversion characteristics and inducing dropout of recorded / reproduced data. Further, deterioration of durability due to thinning of the magnetic layer formed on the non-magnetic support is also an unavoidable problem.

In a coating type magnetic recording medium in which a magnetic material is coated on one surface of a non-magnetic support to form a magnetic layer, a relatively thick lower non-magnetic layer is interposed between the magnetic layer and the non-magnetic support. A multi-layer coating type magnetic recording medium has been proposed. In this multilayer coating type magnetic recording medium, the surface shape of the magnetic layer does not follow the surface shape of the non-magnetic support due to the interposition of the lower non-magnetic layer, and the surface of the magnetic layer can be freely designed. Further, by providing various functions to the lower non-magnetic layer as well as the upper magnetic layer, the characteristics of the recording / reproducing system adopting a linear system for recording / reproducing data in a state where the magnetic recording medium is separated from the magnetic head. It is possible to improve durability against the sliding that occurs between the fixed magnetic head and the magnetic tape running on the magnetic head at high speed.

In a magnetic recording medium such as a magnetic tape, a back layer is provided on the other surface of a non-magnetic support having a magnetic layer on one surface for the purpose of obtaining high reliability. ing. The purpose of providing the back layer on the other surface of the non-magnetic support is to allow the magnetic tape to stably run with respect to the tape running system in the recording / reproducing system.

Minute irregularities are formed on the surface of the back layer provided on the magnetic recording medium, particularly the magnetic tape. The unevenness formed on the back layer has a function of controlling friction with the guide pin with which the running magnetic tape is in sliding contact. Concavities and convexities formed on the back layer are for other purposes to prevent electrification by lowering electric resistance, prevent irregular winding during running by improving winding characteristics, and improve strength of the entire magnetic tape. It is possible to provide assistance for the above, and also to improve the shape of the magnetic tape.

Providing a back layer to a magnetic recording medium including a magnetic tape is a technique required also in a magnetic tape used in a recording / reproducing system adopting a linear system.

[0013]

When a multi-layer coating type magnetic tape as described above is mounted on a recording / reproducing system adopting a linear system and a running test is repeated for a long time,
Scratch-like damage may occur on the surface of the magnetic layer. As a result of investigating the cause of this damage, it was confirmed that the cause was coarse protrusions generated on the surface of the back layer provided on the non-magnetic support constituting the magnetic tape. This phenomenon was more likely to occur than the recording / reproducing system employing the helical scan method described above, but it is considered that this phenomenon is due to the difference between the two systems. In order to increase the transfer speed of the data to be recorded and reproduced, the running speed of the magnetic tape can be increased.
In a system adopting the helical scan method, the magnetic head rotates at a high speed. Therefore, the relative speed between the rotating magnetic head and the magnetic tape can increase the apparent traveling speed of the magnetic tape. It is not necessary to excessively increase the running speed of the magnetic tape.

On the other hand, in the recording / reproducing system adopting the linear system, since the data transfer rate depends only on the magnetic tape speed, the traveling speed of the magnetic tape itself is required to be higher than that of the above-mentioned helical scan system. It will be. Furthermore, in the system that adopted the linear method,
In order to obtain stable running as the speed of magnetic tape increases,
It is necessary to increase the winding tension of the magnetic tape on the tape reel as a tape winding means.
Therefore, in the tape running system of the system adopting the linear system, one surface on which the magnetic layer is formed and the other surface on which the back layer is formed are overlapped with each other while the magnetic tape is wound around the tape reel. When there are coarse protrusions scattered on the surface of the back layer, the stress is concentrated especially on the coarse protrusions, and the protrusions are excessively pressed against the surface on which the magnetic layer is formed. This will damage the magnetic layer side. Further, by providing the projections on the back layer, the friction between the back layer and the guide pin that are in sliding contact with each other is reduced, while the friction generated on the surface on which the magnetic layer is formed is also reduced. If the friction generated on the surface on which the magnetic layer is formed becomes excessively low, winding deviation occurs when the magnetic tape is wound on a tape reel, and the coarse protrusions on the back layer surface rub against the surface on which the magnetic layer is formed. This may damage the surface on which the magnetic layer is formed.

In addition, when there are excessive coarse protrusions on the surface of the back layer, the coarse protrusions may be stored in a heat treatment step during the production of the magnetic tape or by being stored for a long time in a state of being wound around a tape reel. Transferring the shape to the surface on which the magnetic layer is formed causes deterioration of electromagnetic conversion characteristics. Furthermore, the strength of the coating film on the non-magnetic support of the magnetic layer decreases at the shape transfer portion and its vicinity due to the coarse protrusions formed on the magnetic layer, and the magnetic force is particularly high on the fixed magnetic head at high speed. In the linear system in which the tape is run, the magnetic layer easily breaks from the portion where the coating strength is reduced.

Therefore, in order to improve the quality of the magnetic tape used in the recording / reproducing system adopting the linear system as described above, the magnetic layer side is not damaged during repeated running, and the magnetic tape is stored for a long time. However, it is necessary to provide the back layer on the magnetic layer side so as to suppress the shape transfer due to the protrusions existing on the back layer side.

The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a magnetic recording medium such as a magnetic tape capable of enduring high-speed running and realizing high-speed data transfer.

Further, according to the present invention, the magnetic layer can be prevented from being damaged due to the back layer provided on the other surface of the non-magnetic support having the magnetic layer provided on one surface, and the durability can be improved. It is an object of the present invention to provide a magnetic recording medium having high reliability.

[0019]

According to the present invention proposed to achieve the above-mentioned object, a nonmagnetic layer comprising a nonmagnetic powder and a binder is formed on one surface side of a nonmagnetic support. In a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is provided on the non-magnetic layer, and a back layer is provided on the other surface side of the non-magnetic support, the surface of the back layer has the following protrusions. The magnetic recording medium has a height distribution range.

The protrusions of 20 nm or more and less than 40 nm are 1.
The number of protrusions of ² / μm ² or less, 40 nm or more, and less than 80 nm is 0.4 / μm ² or less, and the number of protrusions of 80 nm or more, less than 100 nm is 0.02 / μm ² or less, or 100 nm or more does not exist.

The back layer constituting the magnetic recording medium according to the present invention comprises a binder and a non-magnetic powder, and the non-magnetic powder comprises carbon black having an average particle size of 10 to 50 nm and an average particle size of 60 to 100 nm. Made of carbon black.

In the magnetic recording medium according to the present invention, since the surface of the back layer satisfies the above-mentioned condition, the damage to the magnetic layer side is suppressed even when the magnetic recording medium is repeatedly run, and the magnetic recording medium is wound on a winding means such as a tape reel. Even if it is stored for a long period of time, the shape transfer of the protrusions provided on the back layer to the magnetic layer side is suppressed.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The magnetic recording medium 100 according to the present invention is shown in FIG.
As shown in FIG. 3, the non-magnetic support 101 is provided, and one surface of the non-magnetic support 101 is coated with the non-magnetic coating material for the lower layer prepared by dispersing the non-magnetic powder and the binder with the solvent. A non-magnetic layer 102 as a lower coating film is formed on the non-magnetic layer 102, and a magnetic coating material for the upper layer prepared by dispersing magnetic powder and a binder in a solvent is applied on the non-magnetic layer 102 to form the upper magnetic layer 103. Has been formed. That is, the side on which the upper magnetic layer 103 to be the recording layer is formed is
It is a layer of a multilayer coating film.

In the magnetic recording medium 100 according to the present invention, a back coating material prepared by dispersing carbon black, a binder and the like in a solvent is applied to the other surface of the non-magnetic support 101. The back layer 104 is provided.

Specific materials for forming the upper magnetic layer 103 constituting the recording layer of the magnetic recording medium according to the present invention are as follows.

First, the upper magnetic layer 103 is a ferromagnetic powder,
Although it is composed of a binder and the like, as the ferromagnetic powder, any of conventionally used materials such as metal magnetic powder can be used.

The metal magnetic powder forming the upper magnetic layer 103 is, for example, Fe, Co, Ni, Fe-Co, F.
e-Ni, Fe-Co-Ni, Co-Ni, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, Fe-Co-V and the like. Further, for the purpose of improving various characteristics of these metal magnetic powders, metal components such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added to the above metal powders. Of these, F
The e-based magnetic powder has excellent electrical characteristics. In terms of corrosion resistance and dispersibility, Fe-Al system, Fe-Al-Ca
System, Fe-Al-Zn system, Fe-Al-Co system, Fe-
Ni-Si-Al-Zn system, Fe-Ni-Si-Al-
Fe-Al based alloy powder such as Zn-Mn based is preferable. The shape of these ferromagnetic powders has an average major axis length of 0.5 μm or less, preferably 0.01 to 0.4 μm, more preferably 0.01 to 0.25 μm, and an axial ratio (average major axis length). / Average short axis length) is 12 μm or less, preferably 10 μm or less.

In any of the metallic magnetic powders, the saturation magnetization amount (σs) is preferably 70 emu / g or more.
If σs is less than 70 emu / g, sufficient electromagnetic conversion characteristics may not be obtained. The specific surface area by the BET method is 20 to 9 from the viewpoint of enabling recording and reproduction in the high density recording area.
It is preferably 0 m ² / g, further 20 to 40 m
It is more preferably ² / g. This is because when the specific surface area is within the above range, high density recording becomes possible with the formation of fine particles of ferromagnetic powder, and a magnetic recording medium having excellent noise characteristics can be obtained. It is possible to use one type of each ferromagnetic powder, but two or more types may be used in combination.

As the metal magnetic powder, hexagonal ferrite such as barium ferrite or iron nitride can be used. The barium ferrite is barium ferrite in which a part of Fe is replaced by at least Co and Zn, and has an average particle size (diagonal length of plate surface of hexagonal ferrite) of 300 to 900Å and plate ratio ( The value obtained by dividing the length of the diagonal line of the hexagonal ferrite plate surface by the plate thickness is 2.0.
.About.10.0 and holding power of 35 to 120 kA / m are preferable.

Next, as materials other than the ferromagnetic powder constituting the magnetic layer, additives such as a binder, a non-magnetic reinforcing agent, a lubricant, a dispersant, an antistatic agent and a curing agent can be mentioned.

Examples of the binder include vinyl chloride, vinyl chloride copolymer, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid. Ester-acrylonitrile copolymer, acrylic ester-vinyl chloride-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, polyvinyl fluoride,
Vinylidene chloride-allylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene Examples thereof include butadiene copolymer, polyurethane resin, polyester resin, amino resin, synthetic rubber and the like. Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin and urea formaldehyde resin.

These binders should have the dispersibility of ferromagnetic powder.
-SO for the purpose of improving_ThreeM, -OSO_ThreeM, -COO
M, P = O (OM)_TwoHave polar functional groups such as
Good. Where M is a hydrogen atom or Lithium
Alkali metals such as aluminum, potassium and sodium. Change
In addition, as the polar functional group,₁R_Two, -NR ₁
R_TwoR_ThreeA side chain type having a + X- terminal group, NR₁
R_TwoThere is a main chain type of + X-. Where R in the formula₁R
_TwoR_ThreeIs a hydrogen atom or a hydrocarbon group, + X-
Is a halogen element ion such as fluorine, chlorine, bromine or iodine.
Rui are inorganic and organic ions. Also, -OH, -S
There are also polar functional groups such as H, --CN and epoxy groups. these
The amount of polar functional groups is 10^-1-10^-8mol / g
Preferably 10^-2-10^-6mol / g
More preferably.

It should be noted that these binders can be used alone or in combination of a plurality of types. For example, when polyurethane and / or polyester and a vinyl chloride resin are mixed and used, the weight ratio thereof is in the range of 90:10 to 10:90, preferably 7
It is preferably in the range of 0:30 to 30:70. Further, the following resins may be used together in an amount of 50% by weight or less based on the total binder.

The glass transition temperature of the binder is 50 to 70 ° C.
Is preferred. When the glass transition temperature is within this range, the binder can fill fine ferromagnetic powders with good fluidity. Thus, by using a ferromagnetic powder having a pH value of 7 or more and a binder having a glass transition temperature of 50 to 70 ° C., the ferromagnetic powder is well dispersed in the binder. Become. The binder preferably has a number average molecular weight of 5,000 to 200,000, more preferably 10,000 to 100,000, and has a degree of polymerization of about 50 to 1,000.

The above resins are used as the binder, and the amount of these binders to be mixed in the upper magnetic layer 103 is appropriately 8 to 50 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. It is preferably 10 to 25 parts by weight.

As the non-magnetic reinforcing agent, aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, for the purpose of supplementing the coating film strength and improving running durability, Titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile, anatase), and the like, and carbon black and the like for the purpose of preventing static charge of the magnetic layer, reducing the friction coefficient, and improving the coating strength. You can The amount of the non-magnetic reinforcing particles added is 3 to 2 with respect to 100 parts by weight of the ferromagnetic powder.
It is suitable to be 0 part by weight, preferably 5 to 10 parts by weight.

The non-magnetic reinforcing particles have a Mohs hardness of 4 or more,
It is preferably 5 or more, more preferably 6 or more. Further, the non-magnetic reinforcing particles have a specific gravity in the range of 2 to 6, preferably in the range of 3 to 5. Furthermore, the non-magnetic reinforcing particles are
The average primary particles are 0.05 to 0.6 μm, preferably 0.1.
It is preferable that the thickness is 05 to 0.3 μm.

As the lubricant, silicone oil, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing ester, polyolefin, polyglycol, mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester, fatty acid amide, aliphatic amine, olefin oxide, etc. All known materials such as these can be used, and these may be used alone or in combination.

The lubricant may be added to the paint or may be applied to the surface of the magnetic layer in a post process. In particular, when a fatty acid or a fatty acid ester is added to the coating material, the amount of the fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder. Is preferred.

When the amount of the fatty acid added is less than 0.2% by weight, the running property of the magnetic tape is not sufficiently improved, and when it exceeds 10% by weight, the fatty acid excessively stains the surface of the magnetic layer. If it is taken out, the output may be reduced or the coating film itself may be plasticized. When the amount of the fatty acid ester added is less than 0.2% by weight, still durability is particularly insufficient. Also,
If it exceeds 10% by weight, the fatty acid ester may excessively ooze out onto the surface of the magnetic layer, which may cause a decrease in output and plasticization of the coating film. These are preferably used in combination, in which case the weight ratio of fatty acid to fatty acid ester is 10: 9.
0 to 90:10 is preferable.

In the multi-layer coating type magnetic recording medium 100 of the present invention, the effective amount of lubricant on the surface of the magnetic layer that contributes to running durability can be left to supply from the lower non-magnetic layer 102 side described later. Therefore, the upper magnetic layer 10
The amount of lubricant added to 3 and the method of using the lubricant together are not limited to this.

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

As an antistatic agent, Japanese Patent Laid-Open No. 4-2142 is known.
Surfactants such as those described in JP 18 can be used. The addition amount of these antistatic agents is preferably in the range of 0.01 to 40% by weight with respect to the binder. Any conventionally known materials can be used as these additives, and the additives are not limited at all.

Polyisocyanate or the like is used as the curing agent. Examples of polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. To be The weight average molecular weight of these polyisocyanates is preferably in the range of 100 to 3000.

Next, the lower non-magnetic layer 102 will be described.

The lower non-magnetic layer 102 is formed by applying a non-magnetic coating material mainly containing a binder and non-magnetic powder.

Examples of the non-magnetic powder include acicular α-iron oxide, carbon black having a structure structure, monodisperse carbon black, gateless tyl type titanium oxide, anatase type titanium oxide, tin oxide, tungsten oxide, silicon oxide and zinc oxide. , Chromium oxide, cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ-alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate. Etc. can be mentioned. These non-magnetic powders contain Si compounds and A
It may be surface-treated with a 1-compound or the like. The surface treatment is such that the content of Si or Al is 0.1 with respect to the non-magnetic powder
It is preferable to carry out so as to be 10 to 10 wt%.

The shape of the above-mentioned non-magnetic powder may be needle-like or spherical, preferably needle-like. By using the acicular non-magnetic powder, the surface property of the lower non-magnetic layer 102 is improved, and as a result, the surface of the upper magnetic layer 103 laminated thereon is also smooth. However, the average major axis diameter, the average minor axis diameter, and the axial ratio (major axis diameter / minor axis diameter) of the non-magnetic powder are preferably in the following ranges. That is, the average major axis diameter of the nonmagnetic powder is 0.5 μm or less, preferably 0.3 μm or less, and desirably 0.2 μm or less. The average minor axis diameter is 0.1 μm or less, preferably 0.06 μm or less. A suitable axial ratio is 2 to 20, preferably 5 to 10. The specific surface area is 1
It may be 0 to 250 m ² / g, preferably 30 to 100 m ² . When the non-magnetic powder having the above-mentioned average major axis diameter, average minor axis diameter, axial ratio and specific surface area is used, the surface of the upper magnetic layer laminated thereon is also in a good state.

These non-magnetic powders may be used alone or in combination of plural kinds. When used in combination, it is necessary to pay attention to the size of the particles used in combination, and in order to ensure surface smoothness after coating, the average particle size (for acicular particles, the average major axis length) is 0.3 μm or less. It is preferably 0.2 μm or less. The specific surface area is 10 to 250 m ² / g, preferably 30 to 1
It is preferably 00 m ² / g.

The amount of the nonmagnetic powder mixed in the lower nonmagnetic layer 102 is 50 to 99% by weight, preferably 70 to 95% by weight, based on the total amount of all components constituting the nonmagnetic layer.
Is appropriate. By setting the mixing amount of the non-magnetic powder within this range, the surface properties of the lower non-magnetic layer and the upper magnetic layer become good.

As the binder, any of the resins exemplified as the material forming the upper magnetic layer 103 can be used. The amount of the binder mixed is 5 to 150 parts by weight, preferably 10 to 120 parts by weight, based on 100 parts by weight of the non-magnetic powder.

Further, similar to the upper magnetic layer 103, additives such as a non-magnetic reinforcing agent, a lubricant, a dispersant, an antistatic agent and a curing agent may be added to the lower non-magnetic layer 102. The lubricant can be applied to the surface of the magnetic layer in a later step as described above.

Next, the back layer 104 will be described.

The back layer 104 is formed by applying a non-magnetic coating material mainly containing a binder and a non-magnetic powder. For the back layer 104, carbon black and graphite are mainly used as the non-magnetic powder mainly for the purpose of preventing static electricity, and a non-magnetic reinforcing agent can be used as an additive for obtaining a predetermined strength.

As the non-magnetic reinforcing agent, specifically, Ti
O ₂ , TiO, ZnO, CaCO ₃ , CaO, Sn
O ₂ , SiO ₂ , α-Fe ₂ O ₃ , Cr ₂ O ₃ , α-A
1 ₂ O ₃ , ZnS, MoS ₂ , BaSO ₄ , CaS
O _4, MgCO _3, etc. BN and SiC and the like.
Among these non-magnetic powders, carbon black, graphite, ZnO, TiO ₂ , BaSO ₄ , CaSO
It is preferable to use ₄ as one kind or a combination thereof. The shape of the particles of the non-magnetic powder is not limited, and various commonly used shapes such as spherical shape, needle shape, plate shape, and dice shape can be used.

In the present invention, the distribution of the protrusions formed on the surface of the back layer 104 has the following condition, that is, 20 nm.
As described above, the number of protrusions of less than 40 nm is 1.2 / μm ² ,
0.4 protrusions of 40 nm or more and less than 80 nm / μm ²
And the number of protrusions of 80 nm or more and less than 100 nm is 0.0
The size of the carbon black and the non-magnetic reinforcing material to be used was defined in order to satisfy the condition that the number of protrusions is ² / μm ² and there is no protrusion of 100 nm or more.

That is, in the carbon black, it is preferable to use fine particle carbon black having an average particle size of 10 to 50 nm and medium particle diameter carbon black having an average particle size of 60 to 100 nm in combination. Is more preferably used. The non-magnetic reinforcing material preferably has a Mohs hardness of 5 to 9 and an average powder size of 10 to 300 nm.
If the average powder size is smaller than 10 nm, it becomes difficult to obtain the effect as a reinforcing agent, and if it is larger than 300 nm, the surface property may be impaired.

As the binder and the dispersant, any of the resins exemplified for the upper magnetic layer may be used as long as the surface condition of the back layer satisfies the condition that the projection distribution in the range described in the claims is obtained. It is possible. Above all, the durability and the running property are improved by using the polyester or the polyurethane resin in combination, and the performance as the magnetic recording medium is exhibited. Considering thermal decomposition, hydrolysis stability and the like, a polyester polyurethane resin, more preferably a polycarbonate polyurethane resin is particularly preferable. Further, if a trifunctional isocyanate compound, for example, a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate, or isocyanurate, which is a cycloaddition polymer of 3 mol of diisocyanate, is used in combination as a crosslinking agent, the durability is improved. Etc. can be further improved.

Further, an additive such as a lubricant may be added to the back layer as in the upper magnetic layer. Regarding the lubricant, it is also possible to apply it to the surface of the back layer in a later step as described above.

Using the above materials, the upper magnetic layer 1
03, to form the lower non-magnetic layer 102 and the back layer 104, the upper layer magnetic paint constituting the upper magnetic layer 103, the lower non-magnetic coating constituting the lower non-magnetic layer 102, and the back layer constituting the back layer 104. Adjust each layer paint.

The magnetic coating material for the upper layer is prepared by kneading or mixing various additives such as the ferromagnetic powder, the binder, the non-magnetic reinforcing agent, the lubricant, the dispersant, the antistatic agent and the curing agent, which are exemplified above, together with the solvent. After adjusting the high-concentration magnetic paint, the high-concentration magnetic paint is diluted and dispersed to adjust.

Similar to the magnetic coating material for the upper layer, the non-magnetic coating material for the lower layer is prepared by kneading or mixing the above-exemplified non-magnetic powder, binder and various additives with a solvent to prepare a high-concentration non-magnetic coating material. It is adjusted by diluting and dispersing this high concentration non-magnetic paint.

The back layer paint is the same as the upper layer magnetic paint,
After adjusting the high-concentration back paint by kneading or mixing the carbon black powder exemplified above with the non-magnetic reinforcing agent, binder and various additives with the solvent, adjust by diluting and dispersing this high-concentration back paint. To be done.

As the solvent used for forming the paint, an organic solvent usually used in this type of magnetic recording medium can be used, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. Solvents, alcohol solvents such as methanol, ethanol, propanol, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, etc. Ether solvents, aromatic hydrocarbon solvents such as benzene, toluene, xylene,
Examples thereof include halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and chlorobenzene, which are appropriately mixed and used.

On the other hand, as the non-magnetic support 101, for example, polyesters such as polyethylene terephthalate,
Examples thereof include polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, plastics such as polyamide and aramid resin. These non-magnetic supports 101 may have a single-layer structure or a multi-layer structure. Further, for example, surface treatment such as corona discharge treatment may be applied. The thickness of the non-magnetic support is
30 μm to 10 mm is preferable.

Next, the magnetic tape manufacturing method of the present invention will be described.

First, as described above, the upper layer magnetic coating material, the lower layer non-magnetic coating material, and the back layer coating material are prepared. At this time, the magnetic powder, the binder and the like are, for example, a continuous twin-screw kneader, a continuous twin-screw kneader capable of diluting in multiple stages, a kneader, a pressure kneader, a roll kneader, etc., for example, JP-A-4-214218.
Any of the kneading machines described in the publication can be used. After that, also in the coating material producing step, in the dispersing step, it is dispersed using a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, an agitator, a homogenizer, an ultrasonic disperser or the like.

In the production of this magnetic tape, the lower non-magnetic layer and the upper magnetic layer are formed by simultaneously coating the magnetic coating and the non-magnetic coating prepared as described above on the non-magnetic support in multiple layers. When the non-magnetic coating material and the magnetic coating material are simultaneously applied in multilayers on the non-magnetic support, for example, a die coater is used. Examples of the lip structure of the die coater include a 2-lip method, a 3-lip method, a 4-lip method, and the like.

Generally, when the lower non-magnetic layer 102 and the upper magnetic layer 103 are formed on the non-magnetic support 101, the so-called wet-on-dry coating method, in which coating and drying are performed one by one, is not dried. There is a so-called wet-on-wet coating method, which is a method in which the upper magnetic layer 103 is overlaid on the lower non-magnetic layer 102 in a wet state. When manufacturing the above-mentioned magnetic recording medium, it is preferable to perform simultaneous wet multi-layer coating by a wet-on-wet multi-layer coating method from the viewpoints of coating film homogeneity, adhesiveness between upper and lower interfaces, and productivity.

When the back layer 104 is formed on the other surface of the non-magnetic support 101, the back coating material forming the back layer 104 is applied onto the non-magnetic support 101. As this coating method, any conventionally known coating method such as a one-lip type die coater, a gravure coating method, a blade coating method, and a paint extrusion method can be used.

The upper magnetic layer 103 and the lower non-magnetic layer 102 formed on one surface of the non-magnetic support 101, and the back layer 104 formed on the other surface of the non-magnetic support 101.
Any of may be applied first, and it is also possible to provide an application device on both surfaces of the non-magnetic support 101 and apply simultaneously.

That is, as shown in FIG. 2, this coating film forming system includes a supply roll 1 and a winding roll 2, and the raw material 3 of the non-magnetic support 101 wound around the supply roll 1 is used.
Is fed out from the supply roll 1 toward the take-up roll 2. A coating device 4, an orientation magnet 5, a dryer 6, and a plurality of coating devices for forming a coating film on the raw material 3 along a traveling path of the raw material 3 from the supply roll 1 to the winding roll 2. The calendar device 7 composed of the rolls is arranged in this order.

In the coating film forming system having the structure as shown in FIG. 2, first, the magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer are applied to the one surface of the raw material 3 in multiple layers by using the coating device 4. . The coating device 4 used here is provided with an extrusion coater 8 for lower layer coating material for applying the lower layer coating material and an extrusion coater 9 for upper layer coating material for applying the upper layer coating material. As shown in FIG. 2, these extrusion coaters 8 and 9 are provided with slits 8a and 9a for extruding the paint at the tip end facing the non-magnetic support 101, and a paint reservoir 8b into which the paint is supplied. 9b is provided. The paint supplied to the paint reservoirs 8b and 9b is pushed out to the tip of the coater through the slits 8a and 9a.

On the other hand, the non-magnetic support 10 to which the paint is applied
The raw material 3 constituting 1 is unwound from the supply roll 1 and is wound up by the winding roll 2, so that the raw material 3 is fed from the lower layer extrusion coater 8 to the upper layer along the tips of the extrusion coaters 8 and 9. The extrusion coater 9 is driven in the direction of arrow A in FIG.

On the surface of the raw material material 3 thus running, the lower layer coating extruded from the slit portion 8a of the lower layer extrusion coater 8 as shown in FIG. 3 is applied to form the lower non-magnetic layer 102. The coating film 10 is formed, and the upper layer coating material extruded from the slit portion 9a of the upper layer extrusion coater 9 is applied onto the lower layer coating film 10 in a wet state to form the upper layer coating film 11 to be the upper magnetic layer 103. That is,
Two layers of coating film are successively formed on one surface of the raw material 3.

The raw material 3 on which the upper coating film 11 and the lower coating film 10 are formed is run from the orienting magnet 5 toward the dryer 6 and then fed into the calender device 7 for calender treatment. After that, it is wound around the winding roll 2.

The winding roll wound with the raw fabric material 3 having the upper coating film 11 and the lower coating film 10 formed thereon is used as a supply roll, and the back layer 104 is formed on the other surface of the non-magnetic support 101. It is mounted on the supply side of the coating film forming system for In the coating film forming system used for forming the back layer 104, a back layer extrusion coater is attached in place of the upper layer extrusion coater 8 and the lower layer extrusion coater 9. Also when the back layer 104 is formed using this coating film forming system, as in the case of forming the upper layer coating film 11 and the lower layer coating film 10 described above, the raw material 3 is fed from the supply roll 1 and the winding roll 2 is provided. The non-magnetic coating material mainly composed of the binder and the non-magnetic powder is applied by traveling along the tip portion of the back layer extrusion coater by performing the winding operation by the coating film forming the back layer 104. Is formed. The non-magnetic support 101 on which the coating film forming the back layer 104 is formed by the back layer extrusion coater is wound around the winding roll 2 via the dryer 6 and the calender roll device 7.

In the above description, the lower layer coating film 10 and the upper layer coating film 11 are formed on one surface of the raw material 3, and then the coating film constituting the back layer 104 is formed on the other surface. However, this formation order may be any first, and an extrusion coater for forming the upper layer coating film, the lower layer coating film, and the coating film for the back layer is provided in the same coating film forming system, and they are simultaneously formed in a series of steps. It may be done.

As shown in FIG. 3, the coating film forming system described above is provided with the lower layer coating extruding coater 8 and the upper layer extruding coater 9 independently of each other. An integral type extrusion coater 19 may be used as shown in FIG. 1 for further coating the raw material 3 with a coating material for forming a coating film forming an upper coating film, a lower coating film and a back layer. In addition to the extrusion coater as described above, a gravure roll, a blade coater, an air doctor coater, an impregnation coater, or the like can be used.

In the coating film forming system shown in FIG. 2 described above, the lower layer coating extruding coater 8 and the upper layer extruding coater 9 are arranged separately in the running direction of the raw material 3 constituting the non-magnetic support 101. Therefore, the non-magnetic paint for the lower layer and the magnetic paint for the upper layer are sequentially applied.
By using the integrated extrusion coater 19 in which the slit portions 8a and 9a are provided close to each other, the lower layer coating material and the upper layer coating material may be simultaneously applied.

That is, in the integral type extrusion coater 19 shown in FIG. 4, the lower layer slit portion 8a and the upper layer slit portion 9a through which the coating material is extruded are formed close to the tip portion,
The lower layer paint reservoir 8b to which the respective paints are supplied inside the coater 19 on the back side of the slit portions 8a and 9a,
An upper layer paint reservoir 9b is provided.

The integrated extrusion coater 19 shown in FIG.
Is a paint reservoir 8b formed inside the coater 19,
The lower layer coating material and the upper layer coating material respectively supplied to 9b are extruded to the tip portion of the coater 19 through the slit portions 8a and 9a. On the other hand, the raw material 3 to which the coating material is applied is directed along the tip of the extrusion coater 19 from the lower layer slit portion 8a toward the upper layer slit portion 9a in the direction of arrow A in FIG.
Is driven in the direction.

In the non-magnetic support 101 running along the tip of the integrated extrusion coater 19, when passing through the lower layer slit portion 8a and the upper layer slit portion 9a,
The lower layer paint extruded from the lower layer slit portion 8a is applied, and the upper layer slit portion 9a is applied on the lower layer paint.
The upper layer coating material extruded from is applied to form a two-layer coating film at the same time.

The integrated extrusion coater 19 shown in FIG. 4 is installed in place of the lower layer paint extrusion coater 8 and the upper layer extrusion coater 9 shown in FIG. Other configurations shown in 2 can be used as they are.

The calender roll device used in the coating film forming system is a non-magnetic support 101 in which heat-resistant resin rolls made of polyamide, epoxy, etc. are alternately installed and the coating rolls are sandwiched between them to apply pressure and temperature.
Although the raw material 3 constituting the above is run to perform the calendering process, the calendering roll device for performing the calendering process may use a steel roll instead of the resin roll.

As described above, the raw roll in which the lower layer non-magnetic coating material and the upper layer magnetic coating material are applied to one surface of the raw material 3 and the back layer forming coating material is applied to the other surface are
After being placed in an oven to cure each paint layer, it is cut into a predetermined width to form a magnetic tape as a magnetic recording medium.

[0088]

EXAMPLES Examples of the present invention will be described below.

First, according to the following composition, an upper magnetic coating material for forming the upper magnetic layer 103 provided on one surface of the non-magnetic support 101 of the magnetic recording medium 100, and a non-magnetic layer as a lower coating film. Each component of the lower layer non-magnetic coating material forming 102 was weighed and kneaded and dispersed using a kneader and a sand mill to prepare an upper layer magnetic coating material and a lower layer non-magnetic coating material.

Example 1 Composition of Magnetic Coating Material for Upper Layer P / B Ratio = 6 Ferromagnetic Iron Powder (Specific Surface Area by BET Method: 60 m2 / g, Coercive Force: 18200e) 100 parts by weight Sodium sulfonate group-containing polyurethane resin 4 parts by weight Vinyl chloride resin containing potassium sulfonate group 16 parts by weight Myristic acid 3 parts by weight Carbon black Asahi 50 4 parts by weight α-alumina (average particle size 0.20 μm) 5 parts by weight Butyl stearate 3 parts by weight Heptyl stearate 3 Parts by weight Methyl ethyl ketone 200 parts by weight Toluene 150 parts by weight Cyclohexanone 200 parts by weight Composition of non-magnetic coating material for lower layer P / B ratio = 6 α-Fe ₂ O ₃ (specific surface area by BET method 52 m ² / g) 100 parts by weight Sodium sulfonate Group-containing polyurethane resin 4 parts by weight Potassium sulfonate group-containing Vinyl resin 16 parts by weight Carbon black (Ketjenblack EC) 8 parts by weight α-alumina (average particle size 0.20 μm) 3 parts by weight Butyl stearate 3 parts by weight Heptyl stearate 3 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 50 parts by weight Parts cyclohexanone 100 parts by weight Further, 10 parts by weight of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the dispersion liquid of the upper magnetic coating material and the lower non-magnetic coating material.

Further, in accordance with the following composition, each component of the back layer coating material was weighed and kneaded and dispersed using a kneader and a ball mill to prepare a back layer coating material.

Composition of coating for back layer Carbon black powder (average particle size: 20 nm) 100 parts by weight Polycarbonate polyurethane (glass transition temperature 55 ° C.) 70 parts by weight Nitrocellulose resin 30 parts by weight Titanium oxide (average particle size: 200 nm) 5 parts by weight Part Methyl ethyl ketone 600 parts by weight Toluene 400 parts by weight Further, 1 part of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Co., Ltd.) is used in the dispersion liquid of the back layer paint.
0 part by weight was added.

The magnetic coating material for the upper layer, the non-magnetic coating material for the lower layer, and the coating material for the back layer, which were prepared as described above, were dried on a polyethylene terephthalate film having a thickness of 6.2 μm using a coating apparatus shown in FIG. Upper magnetic layer, 10.5 μm
The lower non-magnetic layer was simultaneously coated in multiple layers. At this time, the upper magnetic coating film was randomly subjected to magnetic field orientation treatment while the coating film was in an undried state. Then, it dried and formed the multilayer coating film. The back layer coating material was applied to the surface opposite to the side from which this multilayer coating film was obtained to form a back layer having a dry coating thickness of 0.5 μm. After that, a wide original roll was obtained by performing a surface smoothing treatment using a calender device in which heat-resistant resin rolls and steel rolls were alternately installed under the following conditions.

Treatment temperature: 65 ° C. Treatment pressure (linear pressure): 40 kg / cm Treatment speed: 150 m / min The raw roll thus obtained is left in an oven at 60 ° C. for 20 hours for curing treatment. Done, then
By slitting into a 1/2 inch width, a pancake, which is a wound body of magnetic tape, was produced. The magnetic tape obtained from the pancake was incorporated into a predetermined cartridge to form a tape cartridge, which was used as a sample.

With respect to this sample, the distribution of protrusions of the back layer, the surface roughness of the back layer, the dynamic friction of the back layer, the dynamic friction between the back layer and the magnetic layer (interlayer friction), the transfer amount of the protrusion of the back layer to the magnetic layer after storage, and The electromagnetic conversion characteristics and the running durability test were evaluated.

<Evaluation Method> The above-mentioned measurement method will be described below.

Protrusion distribution in the back layer Using an atomic force microscope (AFM; NanoscopeaIII manufactured by Digital Instruments), the back surface was measured in a tapping mode in the range of 50 μm × 50 μm, and then the image was analyzed to obtain the protrusion height. The distribution was calculated and the number of protrusions per unit area was calculated.

Amount of transfer of back layer protrusion to magnetic layer after storage and electromagnetic conversion characteristics After the tape cartridge was left in an environment of a temperature of 60 ° C. and a relative humidity of 55% for 4 weeks, the magnetic tape was unwound from the cartridge, Observe the magnetic layer surface within 100 m from
The presence or absence of shape transfer by the back layer protrusion was investigated.
Also, the amount of attenuation of reproduction output was measured as the electromagnetic conversion characteristics before and after storage. For playback output, a fixed head tester equipped with an MR head is used, and the magnetic tape feed speed is 4
m / sec, recording wavelength 0.55 μm, recording frequency 7.3 MH
The playback output of z was measured. As the measured value, the result of Example 1 is 0.
Relative comparison was made as dB.

Running Durability Test A running durability test was carried out by mounting a magnetic tape, which is the magnetic recording medium according to the present invention, on an LTO Ultrium 1 drive (manufactured by Seagate Co., USA) under an environment of a temperature of 25 ° C. and a relative humidity of 60%. A test for reproducing recorded data of 100 GB recorded on the magnetic tape was conducted for 48 hours. After this running test, the damage state of the magnetic layer surface was observed.

The LTO Ultrium 1 drive device used here is shown in FIG. As shown in FIG. 5, the drive device 21 includes a supply reel 22 and a take-up reel 23 arranged in parallel, and the magnetic tape 20 is wound between the supply reel 22 and the take-up reel 23. There is. Supply reel 22
The magnetic tape 22 wound around is wound up from the supply reel 22, travels toward the winding reel 23, and is wound around the winding reel 23. In the running path of the magnetic tape 20 from the supply reel 22 to the take-up reel 23, the first tape is provided from the supply reel 22 toward the take-up reel 23.
, A magnetic head 25, and a second guide roller 26. On both sides of the magnetic head 25,
First and second fixed guides 27, 28 are provided. The first and second fixed guides 27 and 28 control the contact pressure or contact state of the traveling magnetic tape 20 with the magnetic head 25.

The magnetic tape 20 mounted on the drive device 21 constructed as described above is unwound from the supply reel 22 and runs toward the take-up reel 23, and the first and first magnetic tapes arranged in the running path. 2 guide rollers 24, 26
The recording data recorded on the magnetic tape 20 is reproduced by slidingly contacting the magnetic head 25 while being guided by the first and second fixed guides 27 and 28.

The magnetic tape 20 is run so that the surface on which the magnetic layer is formed is in sliding contact with the magnetic head 25.

<Second Embodiment> Next, a second embodiment of the present invention will be described. In the magnetic recording medium of Example 2, the back layer coating material was prepared in the same manner as in Example 1 except that 100 parts by weight of carbon black powder having an average particle size of 35 nm was used as the back layer coating material. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating step, a calendering step, and a curing step using the coating film forming system used to manufacture the magnetic recording medium of Example 1, and then a wide original roll was prepared and slit. Through the steps, a magnetic tape was incorporated into a predetermined tape cartridge to prepare a sample.

The same measurement as in Example 1 was performed on the sample thus obtained.

Example 3 As a back layer coating material, 100 carbon black powder having an average particle size of 70 nm was used.
A back layer coating material was prepared in the same manner as in Example 1 except that the parts by weight were used. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating process, a calendering process and a curing process using the coating film forming system used for manufacturing the magnetic recording medium of Example 1, and then a wide raw roll was prepared, After the slitting process, a magnetic tape was incorporated into a predetermined tape cartridge to obtain a sample.

The same measurement as in Example 1 was performed on the sample thus obtained.

Example 4 A back layer coating composition was prepared in the same manner as in Example 1 except that 50 parts by weight of carbon black powder having an average particle size of 20 nm and 50 parts by weight of carbon black powder having an average particle size of 60 nm were used in combination. The layer paint was adjusted. A magnetic coating material for the upper layer and a non-magnetic coating material for the lower layer are also used in Example 1.
Adjusted as above.

These coating materials were subjected to a coating process, a calendering process and a curing process using the coating film forming system used for manufacturing the magnetic recording medium of Example 1, and then a wide raw roll was prepared. After the slitting process, a magnetic tape was incorporated into a predetermined tape cartridge to obtain a sample.

The same measurement as in Example 1 was performed on the sample thus obtained.

[Comparative Examples] Several comparative examples will be described below.

Comparative Example 1 Comparative Example 1 is an example except that 85 parts by weight of carbon black powder having an average particle size of 20 nm and 15 parts by weight of carbon black powder of 90 nm are used together as a back layer coating material. A back layer coating material was prepared in the same manner as in 1. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating step, a calendering step, and a curing step using the coating film forming system used for manufacturing the magnetic recording medium of Example 1, and then a wide raw roll was prepared and slit. Through the steps, a magnetic tape was incorporated into a predetermined tape cartridge to prepare a sample.

The sample thus obtained was measured and evaluated in the same manner as in Example 1.

Comparative Example 2 In Comparative Example 2, as the back layer coating material, the back layer coating material was prepared in the same manner as in Example 1 except that 100 parts by weight of carbon black powder having an average particle size of 80 nm was used. . The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating process, a calendering process, and a curing process using the coating film forming system used to manufacture the magnetic recording medium of Example 1, and then a wide original roll was prepared and slit. Through the steps, a magnetic tape was incorporated into a predetermined tape cartridge to prepare a sample.

The same measurement as in Example 1 was carried out on the sample thus obtained.

Comparative Example 3 A back layer coating composition was prepared in the same manner as in Example 1 except that 95 parts by weight of carbon black powder having an average particle size of 35 nm and 5 parts by weight of 270 nm carbon black powder were used in combination. The layer paint was adjusted. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer are those of Example 1.
Adjusted as above.

These coating materials were subjected to a coating process, a calendering process and a curing process using the coating film forming system used to manufacture the magnetic recording medium of Example 1, and then a wide raw roll was prepared to produce slits. Through the steps, a magnetic tape was incorporated into a predetermined cartridge to prepare a sample.

With respect to the sample thus obtained,
The same measurement as in Example 1 was performed.

Comparative Example 4 Comparative Example 4 is an example except that 85 parts by weight of carbon black powder having an average particle size of 20 nm and 15 parts by weight of carbon black powder of 150 nm are used together as a back layer coating material. A back layer coating material was prepared in the same manner as in 1. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating process, a calendering process and a curing process using the coating film forming system used to manufacture the magnetic recording medium of Example 1, and then a wide raw roll was prepared and slit. Through the steps, a magnetic tape was incorporated into a predetermined cartridge to prepare a sample.

Regarding the sample thus obtained,
The same measurement as in Example 1 was performed.

Comparative Example 5 Comparative Example 5 is an example except that 70 parts by weight of carbon black powder having an average particle size of 35 nm and 30 parts by weight of carbon black powder having an average particle size of 30 nm are used in combination as a back layer coating material. A back layer coating material was prepared in the same manner as in 1. The magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were prepared in the same manner as in Example 1.

These coating materials were subjected to a coating step, a calendering step, and a curing step using the coating film forming system used for manufacturing the magnetic recording medium of Example 1, and then a wide raw roll was prepared and slit. Through the steps, a magnetic tape was incorporated into a predetermined cartridge to prepare a sample.

Regarding the sample thus obtained,
The same measurement as in Example 1 was performed. <Results and Consideration> Table 1 shows the evaluation results, and FIG. 6 is a graph showing the distribution of protrusions on the back layer surface.

In FIG. 6, S ₁ indicates the first embodiment, S ₂ indicates the _second embodiment, S ₃ indicates the _third embodiment, and S
₄ shows Example 4. Further, in FIG. 6, T ₁ indicates Comparative Example 1, T ₂ indicates Comparative Example 2, T ₃ indicates Comparative Example 3, T ₄ indicates Comparative Example 4, and T ₅ indicates Comparative Example 5. .

[0129]

[Table 1]

The back layer has an average particle size of 20 to 70 n.
Examples 1 and 2 using m fine particle carbon black,
In Nos. 3 and 4, the protrusion distribution of the back layer is 20 to 40 nm.
1.2 pieces / μm^TwoBelow, 40nm or more, 80nm
Less than 0.4 protrusions / μm ^TwoBelow 80 nm, 1
0.02 protrusions / μm less than 00 nm^TwoIs
There was no protrusion of 100 nm or more. These sun
In pulling, back protrusion on the magnetic layer after storage
Almost no transfer was seen, and there was no damage on the magnetic surface after running durability.
No image was observed.

On the other hand, in Comparative Examples 1, 2, 3, 4, and 5, the number of protrusions was large as a whole as compared with each of the above Examples of the present invention, and back protrusion transfer to the magnetic layer after storage occurred, It was confirmed that the playback output after storage was reduced. Also, damage due to back protrusions was observed on the entire magnetic surface after running durability. These are caused by the coarse protrusions on the surface of the back layer, and as shown in Table 1, if the distribution is such that protrusions per unit area of 40 nm or more are present more than in the examples, this is easily affected. it is conceivable that.

From the above, as the distribution of protrusions on the surface of the back layer, the number of protrusions of 20 to 40 nm is 1.2 pieces / μm ² or less, 4
A sample having a back layer in which protrusions of 0 nm or more and less than 80 nm are 0.4 / μm ² or less, protrusions of 80 nm or more and less than 100 nm are 0.02 / μm ² or less, and protrusions of 100 nm or more do not exist. In the above, it was found that there was no decrease in the reproduction output after storage due to the protrusions on the surface of the back layer, and damage to the surface of the magnetic layer after the running test could be suppressed.

[0133]

As described above, the present invention can provide a magnetic recording medium such as a magnetic tape capable of withstanding high-speed running and realizing high-speed data transfer, and further, having a magnetic layer on one surface. It is possible to prevent damage to the magnetic layer due to the provision of the back layer on the other surface of the provided non-magnetic support, and to provide a highly reliable magnetic recording medium with improved durability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a magnetic tape which is a magnetic recording medium according to the present invention.

FIG. 2 is a schematic diagram 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.

3 is a cross-sectional view showing an extrusion coater used in the coating film forming system shown in FIG.

FIG. 4 is a cross-sectional view showing another example of an extrusion coater used in the coating film forming system shown in FIG.

FIG. 5 is a plan view showing a tape running system of a drive device used in a running test of a magnetic tape which is a magnetic recording medium according to the present invention.

FIG. 6 is a graph showing the distribution of protrusions on the back layer formed on the magnetic recording medium.

[Explanation of symbols]

100 magnetic recording medium, 101 non-magnetic support, 1
02 lower magnetic layer, 103 upper magnetic layer, 104 back layer

Claims (2)

[Claims] 1. A non-magnetic layer comprising a non-magnetic powder and a binder is formed on one surface side of a non-magnetic support, and a magnetic layer mainly comprising a magnetic powder and a binder is provided on the non-magnetic layer. A magnetic recording medium in which a back layer is provided on the other surface side of the non-magnetic support, wherein the surface of the back layer has the following protrusion height distribution. 1.2 protrusions of 20 nm or more and less than 40 nm / μm ²
Below, 0.4 protrusions of 40 nm or more and less than 80 nm / μm ²
Below, 0.02 protrusions of 80 nm or more and less than 100 nm / μ
There are no protrusions of m ² or less and 100 nm or more. 2. The back layer comprises a binder and a non-magnetic powder, and the non-magnetic powder comprises carbon black having an average particle size of 10 to 50 nm and carbon black having an average particle size of 60 to 100 nm. The magnetic recording medium according to claim 1, wherein: