JP2003272127A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a magnetic recording medium nearly free from occurrence of a reproduction error and having excellent high density recording characteristics. <P>SOLUTION: In the magnetic recording medium having an under coating layer and a magnetic layer provided on one surface of a non-magnetic substrate and a back coating layer provided on the other surface, the magnetic layer and the under coating layer are specified to have ≤0.09 μm thickness and ≤0.9 μm thickness, respectively. A radiation curing resin and a thermoplastic resin are incorporated to at least two layers of the under coating layer, the magnetic layer and the back coating layer. The radiation curing resin to be incorporated has two or more double bonds in a molecule and has a weight average molecular weight of 50 to 300 per double bond. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention
Excellent magnetic recording media, especially coated magnetic recording tapes
Below, it is also called "magnetic tape" or "tape")
About. [0002] Magnetic tapes include audio tapes and video tapes.
Various uses such as tape and computer tape
However, especially in the field of data backup tapes,
With the increase in capacity of hard disks targeted for backup,
No, one with a recording capacity of several tens to 100 GB per volume
It has been commercialized. In addition, large capacity
Backup tapes have been proposed to increase the recording density.
Is essential. [0003] Magnetic tapes corresponding to such a high recording density have been developed.
In the production of the soup, it is necessary to make the magnetic powder
High-density filling, smooth coating, thin magnetic layer
Along with the layering, the thickness of the undercoat layer and the support became smaller.
coming. In order to increase the recording density, the recording
Shorter track pitch along with shorter signal wavelength
To ensure that the playhead can accurately track the track.
A system that also uses a servo track
ing. To ensure the durability of the magnetic recording medium,
Filler with Mohs hardness of 6 or more on magnetic layer and back coat layer
In addition to the method of adding carbon black and carbon black,
By three-dimensionally cross-linking the resin with a cross-linking material,
It has been practiced to prevent powder and non-magnetic powder from falling off. As a method of three-dimensionally crosslinking, a binder is used.
Use resin containing two or more hydroxyl groups,
An isocyanate compound containing two or more cyanate groups
The formation of a crosslinked structure by inducing a rethanation reaction is one thing.
Generally done. In order for this reaction to take place
Is aged at 50-70 ° C for 12-72 hours.
It becomes necessary. Also utilized other thermosetting reactions
Attempts have been made to form a crosslinked structure, but heat aging
The necessary points are the same. [0007] However, in recent years,
As recording densities of recording media have increased, recording wavelengths have become shorter.
Reducing the thickness of the corresponding magnetic layer and reducing the volume of the recording medium itself
Of non-magnetic support, undercoat layer, back coat layer
Thinner thicknesses are being used. As a result,
The thickness of the entire tape is reduced and the cross-linking reaction described above is performed.
Tape may be damaged by heat aging
The tape and head are deformed by heat during recording and playback.
The tendency for contacts to become unstable during
Was. Also, if there is thermal deformation of such a tape, the tape
The servo system described above,
Also becomes unstable. As a result, it was recorded on magnetic tape
Data cannot be read accurately and high-density recording
Even if you design a magnetic tape that is suitable for recording,
The problem of increasing is emerging. [0008] The present invention addresses such problems.
In at least the coating layer of the coating type magnetic recording medium
Some specific vines that do not require heat aging
By using resin, heat change due to heat aging
Shape can be avoided or suppressed beforehand,
Excellent high-density recording characteristics with low frequency of read errors
It is an object of the present invention to realize a magnetic recording medium. [0009] The present invention provides a non-magnetic support.
Apply undercoat containing non-magnetic powder to one side of
The undercoat layer formed by the above, the magnetic powder on the undercoat layer
Formed by applying magnetic paint containing
Layer, the other side is coated with a backcoat paint containing non-magnetic powder
Having a back coat layer formed by
The recording medium is characterized in that it is configured as follows.
I do. That is, the thickness of the magnetic layer is set to 0.09 μm or less.
The thickness of the undercoat layer is set to 0.9 μm or less,
Layer, magnetic layer and back coat layer, at least 2
One layer contains a thermoplastic resin as a binder and a specific release
Radiation curable resin. And, in this case,
As a fixed radiation curable resin, two or more
Having a weight average molecular weight of 50 per double bond.
A radiation curable resin of ~ 300 is used. like this
In this case, the layer containing a specific radiation-curable resin
Not by heat aging but by radiation irradiation
Can cure (crosslink reaction)
Can avoid thermal deformation due to heat aging
You. In addition, use the specific radiation curable resin as above
The reason is that the resin is mainly responsible for the effect of the coating film
This will be described in detail later.
You. A combination of at least two layers as described above;
(1) Undercoat layer and back coat layer, (2) Magnetic layer
And the back coat layer, and (3) any of the undercoat layer and the magnetic layer
Good, but in terms of preventing playback errors due to thermal deformation
Selects a combination of (1) or (2) rather than (3)
The choice is more effective. This is the radiation
The binder resin curing treatment by irradiation is performed on the non-magnetic support
Rather than applying only to the layer on the side (case (3)), both sides
(1) or (2) for the side layer
However, it can prevent thermal deformation more effectively.
And the magnetic layer is usually a so-called wet-on-wet method
Formula (The upper layer is coated and formed while the lower layer is wet)
At the interface between the two.
Part of the layer is mixed,
At least one layer is cured with a binder resin by radiation irradiation.
If the other layer is hardened to some extent
It is presumed. However, the combination of (1) or (2)
In other words, the combination of (1) is more preferable. Normal,
The undercoat layer is thicker than the magnetic layer, and the undercoat layer is
Because it is in direct contact with the non-magnetic support,
Deformation prevention effect obtained by binder resin curing
Is high. Of course, the undercoat layer, the magnetic layer and the backing layer
The above thermoplastics are used as binders in all layers
Resin and specific radiation-curable resin.
Wear. By doing so, the binder resin of each layer is hardened.
Heating aging that was conventionally performed to
It can be unnecessary. That is, on a non-magnetic support
Apply the undercoat layer, magnetic layer and back coat layer, and after drying,
By irradiating the surface with the radiation,
And eliminates the need for conventional heat aging.
As a result, thermal deformation of the magnetic recording medium accompanying the
Contact and servo control instability
Errors can be reduced. The magnetic layer of the magnetic recording medium is crosslinked by radiation polymerization.
For example, Japanese Patent Application Laid-Open No.
No. 92471, JP-A-58-29124,
As described in JP-A-58-32617.
In the past, all attempts have been made,
The upper thick magnetic layer was cured. However,
Sufficiently hardens a coating film containing a large amount of magnetic powder that is difficult to penetrate
Because it was difficult to
Has not yet reached its full potential
Was. In addition, on a non-magnetic support that can support high recording density
An undercoat layer (non-magnetic layer) containing non-magnetic powder and binder is provided.
Of a multilayer structure in which a thin magnetic layer is provided thereon
For example, Japanese Patent Laid-Open No.
No. 1, JP-A-2001-84553, JP-A-200
In the publication of 1-148111, etc.
There is also a proposal to cure the coating of the layer, undercoat layer, backcoat layer
However, they are all radiation-curable resins.
Hardening the coating film using only
Powder, non-magnetic powder, and carbon black
It was not intended for density filling. In the present invention, a thickness of 3 μm or more as described above is used.
Only imperfect curing of hard coatings
No configuration is adopted. Also, the present invention supports high recording density
When possible, include non-magnetic powder and binder on non-magnetic support
An undercoat layer (non-magnetic layer) and a thin magnetic layer thereon
Applied to magnetic recording media having a multilayer structure provided with
However, each coating is simply made using only radiation-curable resin.
Neither is it cured or cured. Departure
Ming uses fine magnetic powder, non-magnetic powder, and carbon black.
Thermoplastics suitable for good dispersion and specific release
As a radiation curable resin, two or more double bonds in the molecule
Having a weight average molecular weight of 50 to 3 per double bond
With a radiation-curable resin of a binder or the like.
Of conventional binder technology
By making the best use of it and performing further radiation curing
Eliminates the need for heat aging and reduces the thickness of the magnetic layer to 0.0
When the thickness of the undercoat layer is 9 μm or less and the thickness of the undercoat layer is 0.9 μm or less,
Even for recording media, thermal deformation is reduced and errors are reduced.
And a high-density recording medium. BEST MODE FOR CARRYING OUT THE INVENTION A coating film of a coating type magnetic recording medium is cured.
Various types of radiation-curable resin
Has been proposed. In particular, the magnetic properties of fine particles contained in the coating film
To disperse powder, non-magnetic powder and carbon black well
Various measures such as introducing polar functional groups into
(JP-A-57-92471, JP-A-6-13)
No. 1651, JP 2001-148111 A
Etc.) However, a thermoplastic tree structurally designed with similar ideas
Not more than fat
Did not. The present inventors attach great importance to this situation, and study diligently.
As a result, conventional thermoplastic resin with excellent dispersibility
Make the most of it and use a specific radiation-polymerizable resin
I chose the policy of That is, the specific radiation-polymerized resin is mainly coated.
It is designed to act to cure the film. In other words,
Radiation to increase the crosslink density of the film to a certain level
Increase the content of double bonds in the crosslinkable resin. The present invention
As a result of the investigations, it was found that one double bond
The weight average molecular weight of the
If a certain amount of is added to the thermoplastic resin, the entire coating film is crosslinked and cured
I knew I could do it. Double bond of radiation curable resin 1
It is preferable that the weight average molecular weight per unit is in this range.
Is that if the weight average molecular weight is less than 50,
It becomes difficult to synthesize the resin.
The amount of addition required for crosslinking increases and the paint disperses.
This is because the state is reduced. The weight average molecular weight per double bond is 50.
1,3-butane as the radiation-curable resin
Diol diacrylate, 1,4-butanediol dia
Acrylate, 1,6-hexanediol diacrylate
G, ethylene glycol diacrylate, diethylene glycol
Recall diacrylate, triethylene glycol dia
Acrylate, tetraethylene glycol diaclair
G, polyethylene glycol diacrylate, propyle
Glycol diacrylate, dipropylene glycol
Diacrylate, tripropylene glycol diacryle
Ethoxylated bisphenol A diacrylate,
Volak diacrylate, propoxylated neopentyl
Bifunctional acrylates such as
And the same bifunctional methacrylates and
Lis (2-hydroxyethyl) isocyanurate tria
Acrylate, trimethylolpropane triacrylate
G, ethoxylated trimethylolpropane triacrylate
G, pentaerythritol triacrylate, propoxy
Trimethylolpropane triacrylate silicide, propo
Xylated glyceryl triacrylate, caprolactone modified
Trimethylol propane triacrylate
Acrylates and trifunctional compounds similar to the above acrylates
Methacrylate, pentaerythritol tetraacryle
, Ditrimethylolpropane tetraacrylate,
Ethoxylated pentaerythritol tetraacrylate,
Dipentaerythritol hydroxypentaacrylate
And dipentaerythritol hexaacrylate
Tetrafunctional or higher acrylate and same as above acrylate
Monomeric such as methacrylates
Rate (methacrylate) and the above monomers
Polyester, polycarbonate, polyurethane
Which backbone has been oligomerized by extending the molecular chain
Available. Used for magnetic layer, undercoat layer and back coat layer
As the thermoplastic resin, vinyl chloride resin, vinyl chloride-
Vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer
Polymer, vinyl chloride-vinyl acetate-vinyl alcohol
Polymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer
Merging, vinyl chloride-hydroxyl group-containing alkyl acrylate
In cellulosic resins such as polymers and nitrocellulose
At least one selected from the group consisting of a polyurethane resin
Combinations are also included. For the magnetic layer and undercoat layer,
Is also a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer.
It is preferable to use the coalescing and the polyurethane resin together. Bag
The kucoat layer contains, among others, cells such as nitrocellulose.
It is preferable to use a loin resin and a polyurethane resin together.
No. Polyurethane resin is polyester polyurethane
Polyether polyurethane, polyether polyurethane
Ter polyurethane, polycarbonate polyurethane,
Examples include polyester polycarbonate polyurethane. COOH, SO as functional groups _Three M, OSO
_Two M, P = O (OM) _Three , OP = O (OM) _Two [this
In these formulas, M is a hydrogen atom, an alkali metal base or an amine.
Represents a salt], OH, NR'R ", N + R '" R ""
R ″ ″ ′ [wherein R ′, R ″, R ′ ″,
R ″ ″ and R ′ ″ ″ represent hydrogen or a hydrocarbon group], d
Bicycles such as urethane resin composed of polymers having a oxy group
Is used. Of using such a binder
Is because the dispersibility of the magnetic powder and the like is improved as described above.
You. When two or more resins are used in combination, the polarity of the functional group
And preferably -SO _Three M groups
Are preferred. The above thermoplastic resin and one double bond
A radiation curable resin having a weight average molecular weight of 50 to 300;
Binder tree used in combination with the magnetic recording medium of the present invention
It is preferable to use a fat, but if necessary, conventionally known,
(Meth) acryloyl-modified vinyl chloride resin, (Meth)
Radiation-curable resin such as acryloyl-modified urethane resin
May be used in combination. The weight average molecular weight per double bond is 50
~ 300 radiation-curable resins are applied to the entire binder resin.
It is preferably used in the range of 5 to 20 parts by weight. this
If the range is less than 5 parts by weight, the entire coating film is crosslinked.
While the density is small and the durability of the coating film is insufficient, 20 parts by weight
Exceeding the limit makes the coating too hard and adheres to the non-magnetic support.
The quality of the powder decreases, or on the contrary, the powder drop increases
It is. These binders are added to the magnetic layer and the undercoat layer.
And magnetic powder, non-magnetic powder, carbon black, etc.
7 to 50 parts by weight, preferably 100 parts by weight of powder
Or in the range of 10 to 35 parts by weight. In particular, magnetic
In the layer, as the binder resin, vinyl chloride resin
5 to 30 parts by weight, and 2 to 20 parts by weight of polyurethane resin
Is most preferably used in combination. Back coat layer
, Powders such as non-magnetic powders and carbon black
40 to 150 parts by weight, preferably 100 parts by weight, preferably
Is 50 to 120 parts by weight, more preferably 60 to 110 parts by weight
Parts by weight, more preferably 70 to 110 parts by weight. Previous
It is preferable that the above range is less than 50 parts by weight.
If the strength of the coating layer is insufficient and exceeds 120 parts by weight,
This is because the friction coefficient tends to be high. Cellulosic tree
30 to 70 parts by weight of fat and 20 to 5 parts of polyurethane resin
It is preferable to use 0 parts by weight. As the magnetic powder contained in the magnetic layer, rare earth
Ferromagnetic iron-based metal powder containing at least one kind of element, and
Having an average major axis length of 50 nm or less can be used.
You. Transition metals such as Mn, Zn, Ni, Cu, Co
It may be included as gold. Among them, Co and Ni are preferred.
Particularly, since Co can improve the saturation magnetization most,
preferable. The amount of the above transition metal element is
Is preferably 5 to 50 atomic%, and 10 to 30 atomic%.
% Is more preferable. As rare earth elements,
Thorium, Ytterbium, Cesium, Praseodymium
, Samarium, lantern, europium, neodymium
, At least one element selected from terbium, etc.
Is used, among which neodymium and samarium
Medium, terbium and yttrium
It is preferable because a magnetic force can be obtained. The above rare earth-iron metal powder contains boron.
You may let it. By adding boron, the average particle size
Is 50 nm or less in granular or elliptical ultrafine particles.
You. The amount of the rare earth element is 0.2 to 20 atomic% with respect to iron,
It is preferably 0.3 to 15 atomic%, more preferably 0.5 to 10 atomic%.
Atomic%, and the amount of boron is
0.5 to 30 atom%, preferably 1 to 25 atom based on iron
%, More preferably 2 to 20 atomic%. Both atoms above
% Is a value measured by fluorescent X-ray analysis (Japanese Patent Laid-Open No.
001-181754). In this specification, the average of the magnetic powder is used.
The particle size refers to the transmission electron microscope (TEM) magnification
The particle size of a photograph taken at a magnification of 100,000 times was
It is obtained by an average value of zero. Residual magnetic flux density and magnetic layer thickness in the longitudinal direction of the tape
The product of the thicknesses is preferably 0.0018 to 0.05 μTm,
036 to 0.05 μTm is more preferable, and 0.004 to 0.0 μm.
5 μTm is more preferred. This range is preferred because
If it is less than 0.0018 μTm, the reproduction output by the MR head
Is smaller than 0.05 μTm,
This is because the raw output is easily distorted. From such a magnetic layer
The magnetic recording medium can shorten the recording wavelength, and
The playback output when playing back with the R head can be increased, and
The distortion of the reproduction output is small and the output-to-noise ratio can be increased.
Is preferred. Fine magnetic powder having an average major axis length of 50 nm or less
In order to highly fill and highly disperse
It is preferable that the coating is produced in the steps as described above. Kneading
As a pre-process, the granules of magnetic powder are broken using a crusher.
And then use a mixer to mix phosphoric acid-based organic acids and binder
Mixed with resin, surface treatment of magnetic powder, mixed with binder resin
There is provided a step of performing the joining. As a kneading process, continuous twin-screw mixing
Solid content concentration of 80 to 85% by weight with magnetic machine
Kneading with a binder resin ratio of 17 to 30% by weight.
U. As a post-process of the kneading process, a continuous twin-screw kneader is used.
Or at least one time using another dilution device.
Knead and dilute by adding indah resin solution and / or solvent
Process, sand media and other small media rotating type dispersion equipment
The paint is dispersed by a dispersion step according to the present invention. The radiation used in the present invention may be an electron
Rays, γ rays, β rays, ultraviolet rays, etc.
Line. The dose is preferably 1 to 10 Mrad.
~ 7 Mrad is more preferred. In addition, the irradiation energy
(Acceleration voltage) is preferably 30 kV or more. Use ultraviolet light
When using, start photo-generation to generate radicals with ultraviolet light
Need to be used together. As the photoinitiator, 2,2-
Acetophenones, such as diethoxyacetophenone,
Benzophenone, benzyl, benzoin, thiosanton
and so on. Amines such as triethylenetetramine
And sodium diethyldithiophosphate
A sensitizer such as a sulfur compound may be further used.
As the illuminance of ultraviolet rays, 50 to 500 mW / cm ^Two , Irradiation
20-400mJ / cm ^Two Should be in the range of
No. Next, the components of the magnetic recording medium of the present invention
<Non-magnetic support> The thickness of the magnetic support is
Depending on the application, usually 2-5 μm is used.
It is. More preferably, it is 2.5 to 4.5 μm. This range
The thickness of the non-magnetic support is less than 2 μm
Is difficult to form a film, and the tape strength is low, resulting in 5 μm
Exceeds the total thickness of the tape,
This is because the recording capacity is reduced. The Young's modulus of the non-magnetic support in the longitudinal direction is 9.8.
GPa (1000 kg / mm ^Two ) Or more, preferably 10.8G
Pa (1100kg / mm ^Two ) Is more preferred. Non-magnetic
The Young's modulus in the longitudinal direction of the support is 9.8 GPa (1000 kg
/ Mm ^Two The above is good because the Young's modulus in the longitudinal direction is 9.8 GP.
a (1000kg / mm ^Two ), The tape running is unstable
Because it becomes. In addition, helicopter scan type
Is the Young's modulus in the longitudinal direction (MD) / Young's modulus in the width direction
(TD) preferably has a specific range of 0.60 to 0.80.
The Young's modulus in the longitudinal direction / Young's modulus in the width direction is 0.65-0.5.
A range of 75 is more preferred. Young's modulus in the longitudinal direction / width direction
The Young's modulus of the direction should be a specific range of 0.60 to 0.80
If below 0.60 or above 0.80, the mechanism is
At present, it is unknown, but the track of the magnetic head
Large variation in output (flatness) between output side and output side
This is because This variation is due to the longitudinal
The Young's modulus in the modulus / width direction becomes minimum near 0.70. Further
In the linear recording type, the
Although the reason is not clear,
It is preferably from 0.70 to 1.30. Satisfies such characteristics
Biaxially stretched aromatic polyamide base for non-magnetic support
Film and aromatic polyimide film. <Undercoat layer> A smooth undercoat layer having a thickness of 0.09 μm or less
Apply magnetic layer stably and ensure durability of magnetic layer
For this purpose, an undercoat layer is provided. The thickness of the undercoat layer is 0.3 to 0.3.
It is preferable to set it in the range of 9 μm. This range is preferred
What is less, if the thickness is less than 0.3 μm, the effect of reducing the unevenness in the thickness of the magnetic layer
As a result, the effect of improving durability is reduced, and when the thickness exceeds 0.9 μm,
The total thickness of the magnetic recording medium becomes too thick and
This is because the recording capacity is reduced. The non-magnetic particles used in the undercoat layer include acid
There are titanium oxide, iron oxide, aluminum oxide, etc.
Use iron alone or a mixture of iron oxide and aluminum oxide
Is done. Usually, the major axis length is 0.05 to 0.2 μm, and the minor axis length is 5 to 2
Mainly non-magnetic iron oxide of 00nm, particle size as required
0.01 to 0.1 μm carbon black, particle size 0.05 to 0.05
0.5 μm aluminum oxide supplementary content
There are many. Apply undercoat layer smoothly and with less thickness unevenness
In order to achieve the above, the non-magnetic particles and carbon black
It is particularly preferable to use one with a sharp particle size distribution.
No. In place of the undercoat layer containing the above granular particles
And plate-like particles having a particle diameter of 10 nm to 100 nm in the undercoat layer.
May be added. By adding plate-like particles,
Better uniformity of film thickness, surface smoothness, rigidity and dimensional stability
It will be good. The composition of plate-like particles is limited to aluminum oxide
Rare earth elements such as cerium, zirconium, silicon,
Oxide or complex oxidation of elements such as titanium, manganese and iron
Object is used. Plate-like ITO for the purpose of improving conductivity
(Indium, tin composite oxide) particles may be added
No. The undercoat layer is based on the weight of all inorganic powders in the undercoat layer.
To make the plate-like ITO particles 15 to 75% by weight.
To be added. Regarding the production method of these plate-like particles, refer to Japanese Patent Application
2001-296125, Japanese Patent Application No. 2001-2961
26, Japanese Patent Application 2001-296127, Japanese Patent Application 20
01-305138, Japanese Patent Application No. 2001-352092
It is described in gazettes and the like. Also, if necessary,
Black may be added. Carbon black is a particle
Those having a diameter of 10 nm to 100 nm are preferred. Also,
In addition, conventionally known oxidation of iron oxide, aluminum oxide, etc.
Substance particles may be added. In that case, fine particles as much as possible
It is preferable to use those having a small particle size distribution. <Lubricant> The undercoat layer contains the magnetic layer and the undercoat layer.
0.5 to 5.0% by weight of higher fatty acid based on the total powder
0.2 to 3.0% by weight of higher fatty acid ester
When it is contained, the coefficient of friction with the head becomes small, so it is preferable.
Good. The higher fatty acid addition in this range is preferably 0.
If it is less than 5% by weight, the effect of reducing the friction coefficient is small, and
If the content exceeds%, the undercoat layer is plasticized and the toughness is lost.
This is because there is a danger of being caught. In addition, high-grade fat in this range
The addition of fatty acid esters is preferred when less than 0.2% by weight.
Means that the effect of reducing the coefficient of friction is small, and if it exceeds 3.0% by weight,
The tape and head are stuck because the transfer amount to the magnetic layer is too large.
This is because side effects such as sticking may occur. Fat
It is preferable to use a fatty acid having 10 or more carbon atoms as the fatty acid.
Good. As fatty acids having 10 or more carbon atoms, straight-chain,
It may be any of isomers such as Ki and cis-trans,
A linear type having excellent lubrication performance is preferable. Such fat
Examples of the acid include lauric acid, myristic acid, and sulfuric acid.
Thearic acid, palmitic acid, behenic acid, oleic acid,
Nol acid and the like. Among these, Myristi
Acid, stearic acid, palmitic acid and the like are preferred. Magnetic
Fatty acid in fatty layer (same for fatty acid ester)
The amount of fatty acid transferred between the undercoat layer and the magnetic layer
The magnetic layer and the undercoat are not particularly limited.
What is necessary is just to make the addition amount of the fatty acid which combined the layers the said amount.
If fatty acids are added to the undercoat layer, the fatty acids are not necessarily added to the magnetic layer.
Need not be added. The magnetic layer has a weight of 0.5 to 3.0 times the weight of the magnetic powder.
% Fatty acid amide, 0.2 to 3.0% by weight.
When esters of lower fatty acids are included, friction during tape running is reduced.
It is preferable because the friction coefficient becomes small. This range of fatty acids
Preference is given to heads / magnetic at less than 0.5% by weight
Direct contact at the layer interface is easy to occur and the seizure prevention effect is small.
If it exceeds 3.0% by weight, it will bleed out
Because defects such as dropouts may occur.
is there. Fatty acid amides include palmitic acid and stearin
Amides such as acids can be used. In addition, luxury in the above range
Less than 0.2% by weight of fatty acid ester is preferred
The effect of reducing the coefficient of friction is small, and if it exceeds 3.0% by weight,
This is because there are side effects such as sticking to the head. In addition,
Eliminate mutual movement of lubricant in magnetic layer and lubricant in undercoat layer
Not something. <Magnetic Layer> A large-capacity bag exceeding 1 TB
To respond to up-tape, thickness loss and self-reduction
In order to minimize magnetism, the thickness of the magnetic layer should be 0.09 μm or less.
It is preferred to be below. Make the thickness of the magnetic layer within this range.
In order to achieve the above, the number average particle diameter is 50 nm or less
It is preferable to use granular or acicular magnetic powder. The magnetic layer has a particle diameter as described above.
However, plate-like particles having a thickness of 10 nm to 100 nm may be added.
If necessary, a conventionally known abrasive may be added.
But these abrasives include α-alumina,
β-alumina, silicon carbide, chromium oxide, selenium oxide
, Α-iron oxide, corundum, artificial diamond, nitrided
Silicon, silicon carbide, titanium carbide, titanium oxide, diacid
Silicon nitride, boron nitride, etc. with Mohs hardness of 6 or more
Are used alone or in combination. Abrasive particle size and
Therefore, the average particle size is usually 10 nm to 150 nm.
Is preferred. The addition amount is 5 to 20 weight based on the magnetic powder.
% Is preferred. More preferably, it is 8 to 18% by weight. Further, the magnetic layer of the present invention has an improved conductivity.
For this purpose, plate-like ITO particles can be added. Ma
In addition, for the purpose of improving conductivity and surface lubricity, conventionally known capacitors are used.
Carbon black (CB) can be added. this
Acetylene black,
Furnace black, thermal black, etc. can be used
You. Those having a particle diameter of 10 nm to 100 nm are preferred.
This range is preferable because when the particle size is 5 nm or less, the power is reduced.
Dispersion of carbon black is difficult.
Amount of carbon black will need to be added and what
In either case, the surface becomes rough, causing a drop in output.
It is. The addition amount is preferably 0.2 to 5% by weight based on the magnetic powder.
Good. More preferably, it is 0.5 to 4% by weight. <Backcoat layer> Magnetic recording medium of the present invention
The other surface of the non-magnetic support (the magnetic layer is formed
On the side opposite to the side with
As a back coat layer. Backco
The thickness of the coating layer is preferably from 0.2 to 0.8 μm. This range
The good thing is that if it is less than 0.2 μm, the running performance improvement effect is insufficient.
If the thickness exceeds 0.8 μm, the total thickness of the tape will increase,
This is because the recording capacity of the film becomes small. Back coat
Carbon black (CB) can be added to the layer
You. As carbon black, acetylene black,
Furnace black, thermal black, etc. can be used
You. Usually, small particle size carbon black and large particle size carbon black
Use a rack. Particles of small particle size carbon black
Those having a diameter of 5 nm to 200 nm are used.
Those having a thickness of 0 nm to 100 nm are more preferable. This range
More preferably, when the particle size becomes 10 nm or less, the carbon
Is difficult to disperse, and when the particle size is 100 nm or more,
It is necessary to add a large amount of carbon black,
In either case, the surface becomes rough and set off to the magnetic layer
Boss) is the cause. Large particle size carbon black
5-15% by weight of the small particle size carbon black
Uses a large particle size carbon black with a diameter of 300 to 400 nm
As a result, the surface does not become rough, and the effect of improving the running performance also increases.
You. Small particle size carbon black and large particle size carbon black
The total amount added is 60 to 98 weights based on the weight of the inorganic powder.
%, Preferably 70-95% by weight. Ba
The center line average surface roughness Ra of the back coat layer is 3 to 8 nm.
Preferably, 4-7 nm is more preferable. Further, the back coat layer has strength enhancement and size.
For the purpose of legal stability, the carbon black back
A plate-like particle of 10 nm to 100 nm different from the coat layer
A main backcoat layer may be provided. Of plate-like particles
The components are not limited to aluminum oxide, but are
Earth element, zirconium, silicon, titanium, manganese, iron
An oxide or a composite oxide of such an element is used. Bag
In order to improve the conductivity, the plate coat ITO (ink)
Dymium, tin composite oxide) particles can be added
You. In that case, the weight of all inorganic powders in the back coat layer
Based on the basis, 60 to 95% by weight of plate-like ITO particles
It is better to add it. If necessary, a particle size of 10
carbon black with a particle size of 0.1 μm to 100 nm
Iron oxide of m to 0.6 μm may be added. The amount added is
2 to 40 based on the weight of all inorganic powders in the coating layer
% By weight, more preferably 5 to 30% by weight. For the back coat layer, a binder resin is used.
Therefore, the same resin as used for the magnetic layer and the undercoat layer described above is used.
Can be used, but among these, the friction coefficient is reduced and
Cellulose-based resin and polyurethane-based
It is preferable to use a resin in combination with the resin. Binder tree
The content of the fat is usually between the carbon black and the inorganic
40 to 15 based on 100 parts by weight of the total amount with the nonmagnetic powder
0 parts by weight, preferably 50 to 120 parts by weight, more preferably
60 to 110 parts by weight, more preferably 70 to 11 parts by weight.
0 parts by weight. The above range is preferably 50 parts by weight.
If less than 12, the strength of the back coat layer is insufficient, and
If the amount exceeds 0 parts by weight, the friction coefficient tends to increase.
You. 30 to 70 parts by weight of cellulose resin, polyurethane
It is preferable to use 20 to 50 parts by weight of the resin. The back coat layer is formed by crosslinking and curing the coating film.
For this purpose, use the same radiation-curable resin as the magnetic layer and the undercoat layer.
It is preferred to use. The amount of radiation curable resin
5 to 30 parts by weight with respect to 100 parts by weight of resin
, Preferably 7 to 25 parts by weight, more preferably
The preferred amount is 10 to 20 parts by weight. The above range is preferred
When the amount is less than 7 parts by weight, the coating strength of the back coat layer is weak.
If it exceeds 25 parts by weight, it will not react to SUS.
This is because the coefficient of friction increases. <Organic solvent> Magnetic paint, primer paint, bag
Examples of the organic solvent used for the coating material include, for example,
Ethyl ketone, cyclohexanone, methyl isobutyl
Ketone solvents such as ketone, tetrahydrofuran, geo
Ether solvents such as xane, ethyl acetate, butyl acetate
And the like. These solutions
The agents are used alone or as a mixture, and
Used as a mixture. Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these. The implementation
Parts in Examples and Comparative Examples indicate parts by weight. Example 1 << Synthesis of Ultrafine Granular Magnetic Powder >> 0.098 mol of iron nitrate
(III), 0.042 mol of cobalt nitrate and 0.002 mol of
Dissolve neodymium nitrate in 200cc of water and dissolve nitrate in water
A liquid was prepared. Separately from this nitrate aqueous solution, 0.4
Two moles of sodium hydroxide were dissolved in 200 cc of water.
This aqueous solution of sodium hydroxide is converted to the above aqueous solution of nitrate.
In addition, stir for 5 minutes, and water of iron, cobalt and neodymium
An oxide formed. After washing this hydroxide with water, filtration
To remove the hydroxide. This hydroxide (containing water
State), add 150 cc of water and 0.1 mol of boric acid.
Of iron, cobalt and neodymium in an aqueous boric acid solution
The hydroxide was redispersed. Disperse the dispersion at 90 ° C for 2 hours
After heat treatment, wash with water to remove excess boric acid.
Dry at 0 ° C. for 4 hours, iron and cobalt containing boric acid
And a hydroxide composed of neodymium. This hydroxide is placed in air at 300 ° C. for 2 hours.
After heating and dehydrating for a while, heat at 450 ° C for 4 hours in a hydrogen stream.
Thermally reduced, neodymium-iron-cobalt-boron magnetic powder
The end. After that, cool to room temperature while flowing hydrogen gas.
And switch to a nitrogen / oxygen gas mixture and raise the temperature to 6 again.
Elevated temperature to 50 ° C, in a nitrogen / oxygen mixed gas stream for 8 hours
After performing the stabilization treatment, the product was taken out into the air. Neodymium-iron-cobalt-bor obtained
The elementary magnetic powder was measured by X-ray fluorescence,
Odium content is 1.9 atom%, cobalt to iron
The content is 40.1 atomic%, and the content of boron with respect to iron is 7.
It was 5 atomic%. This magnetic powder was obtained using a transmission electron microscope.
(Magnification: 100,000 times).
The particles were circular and had an average particle size of 20 nm. Ma
And saturation measured by applying a magnetic field of 1273.3 kA / m.
Magnetization is 19.7 μWb / g (157 emu / g), coercive force
Was 174.3 kA / m (2190 Oe). << Undercoat paint component >> (1)-Acicular iron oxide (average particle size: 100 nm) 68 parts-Granular alumina powder (average particle size: 80 nm) 8 parts-Carbon black (average particle size: 25 nm) 24 parts -2.0 parts of stearic acid-8.8 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO _Three Na group: 0.7 × 10 ^-Four ・ Equivalent / g) ・ 4.4 parts of polyester polyurethane resin (Tg: 40 ° C, contained -SO _Three Na group: 1 × 10 ^-Four ・ Equivalent / g) ・ 25 parts of cyclohexanone ・ 40 parts of methyl ethyl ketone ・ 10 parts of toluene (2) ・ 1 part of butyl stearate ・ 70 parts of cyclohexanone ・ 50 parts of methyl ethyl ketone ・ 20 parts of toluene (3) ・ Dipentaerythritol hexaacrylate (DPHA) 1 .4 parts (weight average molecular weight per double bond is about 100) ・ cyclohexanone 10 parts ・ methyl ethyl ketone 15 parts ・ toluene 10 parts {Magnetic paint component} (1) Kneading step ・ Ultra-fine particle magnetic powder (Ne —Fe—Co—B) 100 parts (Ne / Fe: 1.9 at%, Co / Fe: 40.1 at% B / Fe: 7.5 at%, σs: 19.7 μWb / g (157 emu / g), Hc : 174.3 kA / m (2190 Oe), average axis length: 20 nm)-vinyl chloride-hydroxypropyl alcohol Relate copolymer 14 parts (containing -SO _Three Na group: 0.7 × 10 ^-Four Equivalent / g) 5 parts of polyester polyurethane resin (PU) (contained -SO _Three Na group: 1.0 × 10 ^-Four ・ Equivalent / g) ・ 10 parts of plate-like alumina (average particle diameter: 50 nm) ・ 5 parts of plate-like ITO (average particle diameter: 40 nm) ・ 2 parts of methyl acid phosphate (MAP) ・ 20 parts of tetrahydrofuran (THF) ・ 20 parts of methyl ethyl ketone / cyclohexanone (MEK / A) 9 parts (2) Dilution step ・ 1.5 parts of palmitic amide (PA) ・ 1 part of n-butyl stearate (SB) ・ 350 parts of methyl ethyl ketone / cyclohexanone (MEK / A) (3) Compounding step・ 1.5 parts of dipentaerythritol hexaacrylate (DPHA) (weight average molecular weight per double bond is about 100) ・ 29 parts of methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts of the above undercoat paint component (1) Batch
After kneading with a formula kneader, add (2) and stir
Dispersion treatment was performed with a residence time of 60 minutes using a domill.
(3) was added to the mixture, and the mixture was stirred and filtered to obtain an undercoat paint. Apart from this, the components of the above magnetic paint are
And (1) mixing the components of the mixing step at high speed in advance.
The mixed powder is kneaded with a continuous twin-screw kneader, and (2)
At least two stages with continuous twin-screw kneader
Dilution is performed in the above manner, and the residence time is 45
And then add (3) the ingredients in the compounding process and stir.
-After filtration, it was used as a magnetic paint. The above-mentioned undercoat paint is coated with an aromatic polyamide fiber.
Lum (thickness 3.3 μm, MD = 11 GPa, MD / TD =
0.70, trade name: MICRON, manufactured by Toray)
After drying and calendering on a porous support (base film)
It is applied so that the thickness becomes 0.6 μm, and on this undercoat layer,
Further, the above magnetic paint is subjected to magnetic field orientation treatment, drying, and calendaring.
-The wafer is processed so that the thickness of the magnetic layer after processing is 0.06 μm.
Apply wet-on-wet, apply magnetic field orientation treatment,
Dry using ear and far infrared rays to obtain a magnetic sheet
Was. In addition, the magnetic field orientation treatment is performed before the dryer.
A stone (5kG) is installed, and the finger coating is dried in the dryer.
Two NN counter magnets (5 kG) from 75 cm in front of the storage
The measurement was performed at intervals of 50 cm. Coating speed is 100m / min
And << Coating composition for back coat layer >> 80 parts of carbon black (average particle diameter: 25 nm) 10 parts of carbon black (average particle diameter: 0.35 μm) 10 parts of granular iron oxide (average particle diameter: 50 nm)・ Nitrocellulose 45 parts ・ Polyurethane resin (SO _Three 30 parts of cyclohexanone 260 parts of toluene 260 parts of methyl ethyl ketone 525 parts
After dispersing with a residence time of 45 minutes, dipentaerythris
Litol hexaacrylate (weight per double bond)
Back coat layer with 15 parts of average molecular weight (approx. 100)
After adjusting the paint for filtration and filtering, the magnetic sheet
On the opposite side of the conductive layer, the thickness after drying and calendering is 0.5 μm.
And dried. The magnetic sheet obtained in this manner is
7-stage calender consisting of rolls, temperature 100 ° C, linear pressure 2
Mirror treatment under the condition of 00 kg / cm, N _Two In a gas atmosphere
Electron beam irradiation (5 Mrad) was performed. Electron beam irradiation is magnetic
The test was performed on both the front and back surfaces of the test. Next, the magnetic system
Cut the sheet to 1/2 inch width and cut it at 200m / min
While running, lapping tape
After polishing, blade polishing and surface wiping,
A magnetic tape was produced. At this time, the wrapping tape
K10000, carbide blade for blade, for surface wiping
Using Toray Toraysee (trade name), running tension 0.2
Processing was performed at 94N. The magnetism obtained as above
Embed the tape in the cartridge and insert it into a computer
Made the soup. Example 2: Instead of ultrafine particulate magnetic powder
Ultrafine needle-shaped magnetic powder (average major axis diameter = 45 nm, BET value
= 73m ^Two / G, Hc = 169.5 kA / m (2130O
e), σs = 14.6 μWb / g (116 emu / g),
Co / Fe = 24 at%, Al / Fe = 4.7 at%, Y
/Fe=12.7 at%), except that
Thus, a computer tape of Example 2 was produced. Example 3 Among the components of the magnetic coating amount, dipenta
Lithritol hexaacrylate (DPHA) omitted
Other than the above, the computer of the third embodiment is the same as that of the first embodiment.
Tape was prepared. Example 4: Magnetic coating amount, undercoating paint, back coat
Dipentaerythritol hexa
Acrylate is the same material as polyethylene glycol
And the weight average molecular weight per double bond is
Same as Example 1 except that it was changed to about 250.
Thus, a computer tape of Example 4 was produced. Example 5: Components of paint for back coat layer
Medium, omit dipentaerythritol hexaacrylate
Otherwise, the computer of the fifth embodiment was executed in the same manner as the first embodiment.
A tape for tape was produced. Example 6: In the components of the undercoat paint, dipenta
Implemented except for omitting risuritol hexaacrylate
The computer tape of Example 6 was made in the same manner as in Example 1.
Made. Example 7: Magnetic coating amount, undercoat, backcoat
1-hydroxycyclohexyl
Add 0.1 part by weight of phenyl ketone to replace electron beam irradiation
Instead, UV irradiation is 250mJ / cm ^Two Except for the actual
In the same manner as in Example 1, the computer tape of Example 7 was used.
Produced. Comparative Example 1: Magnetic coating amount, undercoating paint, back coat
Dipentaerythritol hex in the components of the coating for the coating layer
Omit the acrylate and use polyisocyanate instead
Add the same amount and heat aging instead of electron beam irradiation
Same as Example 1 except that the reaction was performed at 70 ° C. for 48 hours.
A computer tape of Comparative Example 7 was produced. Comparative Example 2: Magnetic coating amount, undercoating paint, backcoat
Dipentaerythritol hexa
Acrylate, the backbone of the same material is polyethylene glycol
Weight average molecular weight per double bond
Was changed to about 350 except that
Similarly, a computer tape of Comparative Example 2 was prepared.
Was. The evaluation was performed as follows. <Playback output and error rate> Playback output and error
The rate is LT modified so that thin tape can be measured.
Recording (recording wavelength 0.55 μm) and reproduction using O drive
Sought by. The reproduction output is the tape of Comparative Example 1.
Is 0 dB, and the output degradation amount is
Recording and reproduction were performed 100 times with the initial value of the loop being 0 dB.
Later values. The error rate is output from the drive.
Based on the error information (number of error bits) input,
I asked more. Error Rate = (Number of Error Bits / Number of Write Bits)
The conditions adopted in the comparative examples are shown together. "Magnetism" in Table 1
Layers, undercoat layers, and backcoat layers
The type of binder used is described. "Heat" is thermoplastic
Resin, "EB" stands for radiation-curable resin respectively
"Heat + EB" means thermoplastic resin and radiation-curable resin
It indicates that the fat was used in combination. Also, in the "Curing means" column
"EB" is electron beam irradiation, "UV" is ultraviolet irradiation,
"Heat" means heat aging, respectively. Further tables
The value shown in the column of "Mw" in 1 is the radiation-curable resin.
Certain “dipentaerythritol hexaacrylate (D
PHA) ”in the molecular chain
Weight average molecular weight per double bond. [Table 1] As is apparent from Table 1, the present invention is realized.
Computer tape according to Examples 1 to 7 (magnetic recording medium
Is compared with the computer tape according to Comparative Example 1.
Out because there is no tape deformation due to heat aging.
High force and low error rate. Further, according to Comparative Example 2,
Coatings are better crosslinked than computer tapes
Because of this, the output decrease after 100 runs is small,
The increase in error rate is also small. As described above, according to the present invention, the heating agent
Avoid thermal deformation that may occur when performing zing
Can be suppressed, and the regeneration energy caused by such thermal deformation can be suppressed.
Can be reduced. In addition, the crosslinkability of the coating film is high.
As a result, the durability is also improved. That is, excellent electromagnetic
A magnetic recording medium with conversion characteristics and excellent durability can be obtained.
You. Thereby, for example, in correspondence with a recording capacity of 1 TB or more.
Realize backup tape for computer
be able to.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Naobu Mika             1-88 Ushitora, Ibaraki-shi, Osaka             Kusel Corporation F-term (reference) 5D006 BA13 BA14 BA19 CA05 CC01                       EA01 FA00 FA09

Claims (1)

Claims: 1. An undercoat layer formed by applying an undercoat paint containing nonmagnetic powder to one surface of a nonmagnetic support, and a magnetic undercoat layer formed on the undercoat layer. A magnetic recording medium having a magnetic layer formed by applying a magnetic paint containing powder, and a backcoat layer formed by applying a backcoat paint containing nonmagnetic powder to the other surface, The thickness of the layer is 0.09 μm or less, the thickness of the undercoat layer is 0.9 μm or less, and at least two of the undercoat layer, the magnetic layer and the backcoat layer are radiation-cured. The radiation curable resin has two or more double bonds in the molecule, and the weight average molecular weight per double bond is 50.
A magnetic recording medium having a size of from 300 to 300.