JP2003123224A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has excellent traveling durability, high coating film smoothness and electromagnetic conversion characteristics. SOLUTION: The magnetic recording medium has an under layer containing magnetic powder or nonmagnetic powder and a binder and at least one upper magnetic layers containing ferromagnetic powder and a binder in this order on a nonmagnetic base. The magnetic layer existing at least at the uppermost layer in the upper magnetic layer contains a binder including a polyurethane resin having a glass transition temperature ranging from 100 to 200 deg.C and the magnetic layer existing at the uppermost layer has surface projections of 10 to 20 nm in height at 5 to 1,000 pieces/100k μm<2> on its surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to excellent running durability.
And a magnetic recording medium having electromagnetic conversion characteristics. [0002] 2. Description of the Related Art Magnetic recording media include recording tapes and videos.
With tape or floppy disk
Widely used. Magnetic recording medium is ferromagnetic powder
Non-magnetically supporting a magnetic layer dispersed in a binder (binder)
Laminated on the holder. Magnetic recording media are electromagnetic conversion
High in characteristics such as performance, running durability and running performance
Need to be at a high level. That is, music recording
For audio tapes for sound playback, a higher level of
Sound reproduction capability is required. Also, attach a video tape.
In other words, the electromagnetic conversion characteristics such as excellent reproduction of the original image
It is required to be excellent. Such an excellent power
Magnetic recording media have good running characteristics while having magnetic conversion characteristics
It is required to have line durability. Durability and electricity
Binders also play an important role in improving magnetic conversion characteristics.
Is responsible. Conventional vinyl chloride tree
With fat, cellulose resin, urethane resin, acrylic resin, etc.
Is inferior in wear resistance of the magnetic layer, magnetic tape running system member
There was a problem of polluting. Also, the magnetic head contamination is inferior in electromagnetic conversion characteristics.
This is the cause of Especially with high-density recording equipment
The magnetic head rotation speed is rising and digital video
In the tape recorder, the rotation speed of the magnetic head is 9600 times
1 for consumer use of analog video tape recorder
800 rpm, compared with 5000 rpm for business use
The stage has a high rotational speed, and the magnetic recording medium and magnetic head
The sliding speed is increased. The magnetic head is also thin.
Small ones such as membrane heads are used and magnetic
Magnetic head contamination due to components generated from the recording medium can be improved.
It has been demanded. As a method of improving such problems, hard
A method to increase the hardness of the magnetic layer using a binder
Yes. For example, Japanese Patent Laid-Open No. 11-96539 discloses a DA.
Polyurethane containing imerdiol as the diol component
A magnetic recording medium using a resin as a binder is described.
The Japanese Patent Laid-Open No. 2001-134922 discloses a ring.
Diol compounds with long structures and long alkyl chains and long
Weight average having a predetermined polar group as a chain polyol component
Using a polyol having a molecular weight (Mw) of 400 to 5000
Polyurethane resin is used as a binder. Gala
A polyurethane resin having a high transition temperature (Tg) and a binder
When used, the coating strength at high temperatures is particularly high.
Good running durability can be obtained. However, Tg
To increase it, increase the ring structure and urethane bond components
However, the cyclic structure and urethane bond components are increased.
In this case, sufficient dispersibility can be obtained because solvent solubility decreases.
However, there was a problem that the smoothness of the coating film was lowered. [0005] SUMMARY OF THE INVENTION Accordingly, the object of the present invention is as follows.
Has excellent running durability and high coating smoothness.
To provide a magnetic recording medium having improved electromagnetic conversion characteristics
It is. [0006] Means for Solving the Problems The present inventors have made the above object.
We conducted intensive research to achieve this. As a result, glass
Polyurethane tree having a temperature of 100 to 200 ° C
Contains at least the top magnetic layer as a binder component
To achieve excellent coating strength and magnetic properties of the top layer
By defining the number of microprotrusions present on the layer surface,
Magnetic recording medium with both excellent running durability and electromagnetic conversion characteristics
Find the body and complete the present invention
It came to. That is, the object of the present invention is to (1) Magnetic powder or nonmagnetic powder and particles on a nonmagnetic support
A lower layer containing a mixture and a small amount containing a ferromagnetic powder and a binder.
Magnetic recording medium having at least one upper magnetic layer in this order
And at least the uppermost layer of the upper magnetic layer
The magnetic layer located has a glass transition temperature of 100 to 200 ° C.
A binder comprising a polyurethane resin that is in the range of
The magnetic layer located on the uppermost layer has a height of 10 to 2 on its surface.
5 to 1000 surface protrusions of 0 nm / 100 μm²Have
This is achieved by a magnetic recording medium. A preferred embodiment of the magnetic recording medium of the present invention is as follows.
It is as follows. (2) The polyurethane resin has a cyclic structure and a long chain alkyl.
A polyurethane resin consisting of a diol component having a
A magnetic recording medium according to (1). (3) The magnetic layer has a thickness of 0.05 to 1.0 μm.
The magnetic recording medium according to (1) or (2). [0008] BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a magnetic recording medium of the present invention will be described.
Will be described in more detail. The magnetic recording medium of the present invention is non-
A multilayer magnetic layer or a nonmagnetic layer and a magnetic layer are formed on a magnetic support.
Have a multi-layer structure in the order of
A magnetic layer having a glass transition temperature of 100 to 200 ° C.
A binder containing a urethane is used. Polyurethane
May also be included in the upper magnetic layer other than the top layer
However, it is not substantially contained in the lower layer (magnetic layer or nonmagnetic layer).
Yes. The glass transition temperature of the present invention is applied to the uppermost magnetic layer.
When using a binder containing high polyurethane, the magnetic layer
The elastic modulus at high temperatures of the
The plastic flow of the magnetic layer due to frictional heat generated by sliding
Suppressed, high coating strength was obtained, and excellent running durability
Can be achieved. In particular, the magnetic layer located at the top layer
If the layer is made thinner, the mechanical strength of the magnetic layer will decrease.
The effect of bright polyurethane is that the top magnetic layer is a thin layer
It is remarkable in the case. On the other hand, the top that contacts the head during recording / reproduction
Microprojections with a height of 10 to 20 nm exist on the surface of the magnetic layer
Then, it is known that the electromagnetic conversion characteristics are deteriorated.
  However, polyurethane with a high glass transition temperature is cyclic
Many structures with low solvent solubility such as structures and urethane bonds
Have. Therefore, polyurethane with a high glass transition temperature
When using, the dispersibility of the coating solution decreases, and the surface of the magnetic layer
There is a problem that small protrusions are generated. Therefore, the present invention
In magnetic recording media, it exists on the top surface of the magnetic layer.
5 to 1000 surface protrusions having a height of 10 to 20 nm /
100 μm²By reducing the frequency to
Secured. Furthermore, the number of surface protrusions with a height of 10 to 20 nm
Is within the above range, the friction coefficient during running is reduced.
As a result, the effect of further improving running durability can be obtained.
Can do. That is, in the present invention, a predetermined polymer is used as the binder.
Use urethane resin and specify the number of surface protrusions
From these effects, excellent running durability is achieved. [Polyurethane resin] The upper magnetic layer of the present invention
Of the magnetic layer located at least in the uppermost layer.
The glass transition temperature (Tg) of the urethane resin is 100-
200 ° C., preferably 140-180 ° C.
It is a range. When Tg is less than 100 ° C., coating at a high temperature
Since film strength is reduced, good running durability can be obtained.
If not, dispersibility decreases when the temperature exceeds 200 ° C, electromagnetic conversion
Characteristics and running durability are reduced. Polyurethane of the present invention
Resin has a high glass transition temperature, especially in high temperature environments
Magnetic recording with high durability
Recording media can be obtained. The polyurethane resin of the present invention has a urethane group.
The concentration should be in the range of 2.5 to 6.0 mmol / g
Preferably, more preferably 3.0 to 4.5 mmol / g
It is appropriate that Urethane group concentration is 2.5mm
When it is ol / g or more, the coating film has a high Tg and good durability.
When it is 6.0 mmol / g or less,
Dispersibility is good due to high solvent solubility. Urethane group
If the concentration is too high, it must contain polyol.
Control of molecular weight becomes difficult
Etc., which is not preferable in the synthesis. The weight average molecule of the polyurethane resin of the present invention
The amount (Mw) is in the range of 30,000 to 200,000
Preferably there is, more preferably 50,000-1
A range of 00,000 is appropriate. Molecular weight
If it is 30,000 or more, the coating film strength is high and the durability is good.
If it is 200,000 or less, the solvent can be obtained.
High solubility and good dispersibility. As a polar group of the polyurethane resin of the present invention
Is -SO_ThreeM, -OSO_ThreeM, -PO_ThreeM₂, -COOM
Is more preferable, and -SO is more preferable._ThreeM, -OSO_ThreeAt M
It is appropriate to be. The content of polar groups is 1 × 10^-Five
~ 2x10^-FourIt is preferable that it is eq / g. 1 × 10
^-FiveAdsorbability to magnetic and non-magnetic materials when eq / g or more
Is high and dispersibility is good. On the other hand, 2 × 10^-Foureq / g
If it is below, the solvent solubility is high and the dispersibility is good.
The The OH group content in the polyurethane resin is 1
Preferably 2-20 per molecule, more preferred
Or 3-15 per molecule
The By containing two or more OH groups per molecule,
Reacts well with isocyanate curing agents, so coating strength
And good durability can be obtained. Meanwhile, 1 minute
If it contains 15 or less OH groups per child, the solvent solubility is high.
And dispersibility is good. Used to add OH groups
Examples of the compound include a compound having an OH group of 3 or more functional groups, such as
Trimethylolethane, trimethylolpropane, anhydrous
Trimellitic acid, glycerin, pentaerythritol,
Hexanetriol, trifunctional and polyfunctional branched poly
Ester or polyether ester can be used
The Among these, trifunctional ones are preferable. 4 officials
If it exceeds the capacity, the reaction with the curing agent becomes too fast and the pot
If becomes shorter. Polyurethane resin used in the binder of the present invention
As the polyol component, polyester polyol,
Polyether polyol, polycarbonate polyol
, Polyetherester polyol, polyolefin
Ring structures such as polyols and dimer diols and long chain al
Known polyols such as diol compounds having a kill chain
Can be used. The molecular weight of the polyol is 500
About 2000 is preferable. The molecular weight is within the above range
And increasing the weight ratio of diisocyanate substantially
Can increase the number of urethane bonds, and the interaction between molecules
Strengthen, high glass transition temperature and high mechanical strength
Can be obtained. The diol component has a cyclic structure and a long chain chain.
A diol compound having an alkyl chain is preferred.
Yes. Here, the long-chain alkyl chain is an aryl having 2 to 18 carbon atoms.
Refers to rualkyl group. Has a cyclic structure and a long alkyl chain
And has a bent structure, so it has excellent solubility in solvents.
The As a result, the surface of the magnetic or non-magnetic material in the coating solution
Since the spread of adsorbed urethane molecular chains can be increased,
It has the effect of improving dispersion stability and has excellent electromagnetic conversion characteristics.
Sex can be obtained. In addition, having a ring structure
To obtain polyurethane with higher glass transition temperature
it can. Diol having cyclic structure and long alkyl chain
The compound is particularly preferably a diolation represented by the following formula:
It is a compound. [0017] [Chemical 1] Z is a cyclohexane ring, benzene ring or naphthalene ring
A cyclic structure selected from: R₁And R₂Is carbon number 1
18 alkylene groups, R_ThreeAnd R_FourIs carbon number 2-1
8 alkyl groups. The diol component is contained in the polyurethane resin.
10 to 50 wt% is preferable, and more preferable
Preferably, it is contained in an amount of 15 to 40 wt%. 1
If it is 0 wt% or more, the solvent solubility is high and the dispersibility is good
When Tb is 50wt% or less, Tg is high and durability is excellent.
A coating film having properties is obtained. The polyurethane resin of the present invention contains a chain extender.
In combination with diol components other than the above diol components
You can also. When the molecular weight of the diol component increases,
Inevitably, the diisocyanate content is reduced.
Reduces urethane bonds in the re-urethane and increases the coating strength
Inferior. Therefore, in order to obtain sufficient coating strength,
The chain extender is less than 500 molecular weight, preferably 300
The following low molecular weight diols are preferred. Ingredients
Physically, ethylene glycol, 1,3-propanedio
, Propylene glycol, neopentyl glycol
(NPG), 1,4-butanediol, 1,5-penta
Diol, 1,6-hexanediol, 1,8-oct
Tandiol, 1,9-nonanediol, 2,2-dimethyl
Til-1,3-propanediol, 2-ethyl-2-but
Til-1,3-propanediol, 2,2-diethyl-
Aliphatic glycols such as 1,3-propanediol, siku
Rhohexanedimethanol (CHDM), cyclohexane
Diol (CHD), Hydrogenated Bisphenol A (H-B
PA) and the like and ethylene oxides thereof
Side adduct, propylene oxide adduct, bisphenol
Nord A (BPA), Bisphenol S, Bisphenol
Aromatic glycol such as Ru P, bisphenol F and the like
Ethylene oxide adduct, propylene oxide
Adducts can be used. Particularly preferred is hydrogen
Bisphenol A. Diisodiene used in the polyurethane resin of the present invention
As cyanate, known ones can be used.
The Specifically, TDI (tolylene diisocyanate
G), MDI (diphenylmethane diisocyanate),
p-phenylene diisocyanate, o-phenylene dii
Socyanate, m-phenylene diisocyanate, xy
Lylene diisocyanate, hydrogenated xylylene diisocyanate
Nate and isophorone diisocyanate are preferred. The polyurethane resin of the present invention is vinyl chloride-based.
These synthetic resins may be used in combination. Salts that can be used in combination
The degree of polymerization of the vinyl fluoride resin is preferably 200 to 600,
250 to 450 is particularly preferable. Vinyl chloride resin is
Nyl monomers such as vinyl acetate, vinyl alcohol
, Vinylidene chloride, acrylonitrile, etc.
It can also be The polyurethane resin of the present invention contains vinyl chloride.
Various synthetic resins can be used in addition to the base resin. Example
For example, ethylene / vinyl acetate copolymer, nitrocellulose
Cellulose derivatives such as resin, acrylic resin, polyvinyl chloride
Nil acetal resin, polyvinyl butyral resin, epoxy
Xy resin and phenoxy resin. These can be alone
Combinations can also be used. When other synthetic resins are used in combination, the magnetic layer
The polyurethane resin contained in the binder is 10 to 90 in the binder.
It is preferable that it contains wt%, more preferably
Is an amount of 20-80% by weight. Particularly preferably 25-
The amount is 60% by weight. Vinyl chloride resin is bonded
It is preferable to contain 10-80% by weight in the agent
More preferably, the amount is 20 to 70% by weight. In particular
The amount is preferably 30 to 60% by weight. In addition to the binder of the present invention, the polyiso
Curing agents such as cyanate compounds can be used.
Examples of polyisocyanate compounds include tolylene diisocyanate.
3 moles of cyanate and 1 mole of trimethylolpropane
Reactive organisms (eg, Desmodur L-75 (Bayer
), Xylylene diisocyanate or hexa
Diisocyanates such as methylene diisocyanate
The reaction product of 1 mol of trimethylolpropane and
Burette with 3 moles of xamethylene diisocyanate
Addition compound, 5 moles of tolylene diisocyanate
An anurate compound, 3 moles of tolylene diisocyanate
Isocyanurate of 2 moles of hexamethylene diisocyanate
Acid addition compounds, isophorone diisocyanate and di
List the polymers of phenylmethane diisocyanate
You can. Polyisocyanate compound contained in magnetic layer
The product is contained in the binder in the range of 10 to 50% by weight.
Preferably, it is more preferably 20 to 40% by weight
Range. Also, curing treatment by electron beam irradiation is performed.
In some cases, a reactive double such as urethane acrylate
A compound having a bond can be used. Resin component
And the weight of the hardener (ie binder) is ferromagnetic
Usually in the range of 15 to 40 parts by weight per 100 parts by weight of the powder.
It is preferably within the range, more preferably 20-30.
Parts by weight. In the upper layer, a known binder may be used in combination.
it can. For example, polyester, polycarbonate, polyester
Public using polyols such as ether and polyolefin
Known polyurethane, vinyl chloride, vinyl acetate, vinyl alcohol
Copolymerized with rucol, vinylidene chloride, acrylonitrile, etc.
Combined polyvinyl or the like can be used in combination. [Number of surface protrusions] The top of the magnetic recording medium of the present invention
The magnetic layer located in the layer has a height of 10 to 20 nm on its surface.
5 to 1000 surface protrusions / 100 μm²Have. Further
Preferably, the number of surface protrusions having a height of 10 to 20 nm is 5 to 2.
00 / μm²It is. Surface protrusions with a height of 10-20 nm
The number is 100μm²If it is less than 5 per hit,
The friction coefficient increases and the running durability decreases.
If the amount is too large, the electromagnetic conversion characteristics deteriorate. In addition, height 20nm
If there are many surface protrusions exceeding
Electromagnetic conversion characteristics deteriorate due to increased single loss
The Therefore, the height 2 present in the magnetic layer located at the top layer is 2
It is preferable that there are few surface protrusions exceeding 0 nm. Ma
In order to further improve the electromagnetic conversion characteristics, the height 10
It is preferable that the number of surface protrusions less than n nm is small. The surface protrusions of the magnetic layer located at the top layer are
Magnetic material contained in the upper layer, abrasive, carbon black,
Magnetic or non-magnetic material, abrasive,
-Particle size of inorganic powder such as Bon Black
Prepare the type of binder and lubricant to be dispersed, upper layer liquid, and lower layer liquid
Kneading conditions, dispersion conditions, coating layer thickness, coating drying conditions
Can be controlled according to conditions, calendar conditions, etc.
it can. Specifically, the kneading conditions are as follows when preparing the upper layer coating solution.
The kneading solid content concentration is preferably 75 to 95% by weight.
Yes. Within the above range, the dispersibility is good, and the uppermost layer
The magnetic layer has few surface protrusions and high smoothness.
The The kneading solid content concentration at the time of preparing the lower layer coating solution was 65
It is preferable to set it to -85 weight%. Within the above range
And dispersibility is good, and exists at the interface between the lower and upper layers
There are few microprojections, and as a result, the uppermost layer is present in the magnetic layer
The number of minute projections can be reduced. Dispersion ball
Dispersing machines such as mills, sand grinders, and attritors
Use and disperse the viscosity (solid content concentration) of the coating liquid within the dispersible range.
It is preferable to increase the dispersion share. Distributed
By increasing the hair, it is possible to improve the dispersibility of the coating liquid
it can. The calendar processing condition is that the roll temperature is 60-1
00 ° C, preferably 70-90 ° C, linear pressure 980-49
00 N / cm, preferably 1960 to 4412 N / cm
It is preferable to carry out as Calendar processing with the above conditions
To obtain a coating film with excellent surface smoothness
Can do. Note that the processing rolls are
Resistance of Si, polyimide, polyamide, polyamideimide, etc.
Thermal plastic rolls are used and are metal rolls
It is preferable. As mentioned above, magnetism located in the top layer
Various methods for controlling the number of protrusions on the layer surface
The surface state defined by the magnetic recording medium of the present invention is obtained.
Therefore, use these methods in combination as appropriate
Can do. The surface protrusions of the magnetic recording medium of the present invention are atoms.
Measure using an atomic force microscope (AFM). Specifically, Digit
al Instrument Nanoscope III (Atomic Force Microscope (AFM))
Using a square pyramid SiN probe with a ridge angle of 70 °, 10
μm square (100 μm²) Microprojection height of 10-20
The number of protrusions is measured every 5 nm up to nm. [Ferromagnetic powder] Used in the magnetic recording medium of the present invention
The ferromagnetic powder used is cobalt-containing ferromagnetic iron oxide or strong
S with magnetic alloy powder_BETSpecific surface area of 40-80m²/ G,
Preferably 50-70m²/ G is appropriate
The The crystallite size is 12-25 nm, preferably 13-
22 nm, particularly preferably 14 to 20 nm
Is appropriate. The long axis length is 0.05-0.25μm
Yes, preferably 0.07 to 0.2 μm, particularly preferably
It is preferable that the thickness is 0.08 to 0.15 μm.
The Ferromagnetic powder includes yttrium-containing Fe, F
e-Co, Fe-Ni, Co-Ni-Fe,
The yttrium content in the ferromagnetic powder is based on iron atoms
Yttrium ratio, Y / Fe 0.5 atomic% to 20
Atomic% is preferred, more preferably 5-10 atomic%
It is appropriate to be. If it is 0.5 atomic% or more, it is strong
High σ of magnetic powder_SCan be improved and magnetic characteristics are improved.
Good electromagnetic conversion characteristics can be obtained. 20 atomic% or less
The iron content is appropriate and the magnetic properties are good.
Thus, the electromagnetic conversion characteristics are improved. Furthermore, to 100 atomic% of iron
Within 20 atomic% or less, aluminum, silicon
Elemental, sulfur, scandium, titanium, vanadium, black
Manganese, copper, zinc, molybdenum, rhodium, para
Palladium, tin, antimony, boron, barium, tantalum
Ru, tungsten, rhenium, gold, lead, phosphorus, lanta
, Cerium, praseodymium, neodymium, tellurium, bis
A trout etc. can be included. In addition, there is little ferromagnetic metal powder.
Including water, hydroxide or oxides
Also good. The present invention introduces cobalt and yttrium.
An example of the manufacturing method of the ferromagnetic powder made is shown. Ferrous salt and a
Oxidizing gas is blown into the aqueous suspension mixed with Lucari.
Iron oxyhydroxide obtained as a starting material
An example can be given. This type of iron oxyhydroxide and
Therefore, α-FeOOH is preferable.
Uses Fe (OH) by neutralizing ferrous salt with alkali hydroxide.
₂Aqueous suspension of
There is a first production method that uses needle-like α-FeOOH. one
On the other hand, the ferrous salt is neutralized with alkali carbonate and FeCO_ThreeWater of
A suspension, and an oxidizing gas is blown into the suspension for spinning.
There is a second production method that uses a spindle-shaped α-FeOOH. This
Una iron oxyhydroxide is a ferrous salt aqueous solution and an alkaline aqueous solution.
To obtain an aqueous solution containing ferrous hydroxide,
This is obtained by oxidation by air oxidation or the like.
Are preferred. At this time, Ni salt or C
a salt of alkaline earth elements such as a salt, Ba salt and Sr salt, Cr
Salt, Zn salt, etc. may coexist and such salt is suitable.
By selecting and using the particle shape (axial ratio), etc.
Can be prepared. Ferrous salts include ferrous chloride and ferrous sulfate.
Iron or the like is preferable. As alkali, sodium hydroxide
Ammonia water, ammonium carbonate, sodium carbonate
Etc. are preferred. As a salt that can coexist
Nickel chloride, calcium chloride, barium chloride, salt
Chloride such as strontium chloride, chromium chloride, zinc chloride
preferable. Then, when introducing cobalt into iron,
Before introducing thorium, cobalt sulfate, cobalt chloride
An aqueous solution of a cobalt compound such as
Stir and mix with the slurry. Oxygen containing cobalt
After preparing the iron hydroxide slurry,
Add an aqueous solution containing thorium compound and stir and mix
Can be introduced. The ferromagnetic powder of the present invention contains yttrium or later.
Also neodymium, samarium, praseodymium, lanta
Can be introduced. These are yttrium chloride
Um, neodymium chloride, samarium chloride, praseody
, Lanthanum chloride and other chlorides, neodymium nitrate, gallium nitrate
It can be introduced using nitrates such as dolinium.
These may be used in combination of two or more. Ferromagnetic powder
There are no particular restrictions on the shape of the material, but it is usually acicular, granular,
B-shaped, rice-grained and plate-shaped ones are used. Toku
It is preferable to use acicular ferromagnetic powder. The above resin component, curing agent and ferromagnetic powder
Methyl ether usually used in the preparation of magnetic paints
Tyl ketone, dioxane, cyclohexanone, ethyl acetate
Kneading and dispersing together with a solvent such as ruby to obtain a magnetic paint. For kneading
The dispersion can be carried out according to the usual methods. Magnetic
In the paint, in addition to the above components, α-Al₂O_Three, Cr₂O_Three
Abrasive materials such as carbon black, antistatic agents such as carbon black, fat
Lubricants such as acids, fatty acid esters and silicone oils,
Contains commonly used additives or fillers such as powder
It may be. [Lower layer] Next, the lower layer of the present invention (magnetic layer or non-layer)
The magnetic layer will be described. The lower layer of the present invention is a nonmagnetic layer
In some cases, the non-magnetic powder contained in the lower layer is a metal oxide,
Metal carbonate, metal sulfate, metal nitride, metal carbide, gold
It can be selected from inorganic compounds such as genus sulfides.
As an inorganic compound, for example, α having a gelatinization rate of 90 to 100%
-Alumina, β-alumina, γ-alumina, silicon carbide
Element, chromium oxide, cerium oxide, α-iron oxide, colanda
Silicon nitride, titanium carbide, titanium oxide, dioxide
Silicon, tin oxide, magnesium oxide, tungsten oxide,
Zirconium oxide, boron nitride, zinc oxide, calcium carbonate
Um, calcium sulfate, barium sulfate, molybdate disulfide
Can be used alone or in combination. Special
Preferred are titanium dioxide, zinc oxide, iron oxide,
Barium sulfate, more preferred is titanium dioxide
It is. These nonmagnetic powders have an average particle size of 0.005 to 2
μm is preferred, but non-magnetic with different average particle size if necessary
Particle size can be combined with non-magnetic powders.
The same effect can be obtained by widening the cloth. Tori
Preferably, the average particle size of the nonmagnetic powder is 0.01 μm.
~ 0.2 μm. The pH of non-magnetic powder is between 6-9
Particularly preferred. Specific surface area of non-magnetic powder is 1-100m²
/ G, preferably 5-50m²/ G, more preferably 7
~ 40m ²/ G. The crystallite size of non-magnetic powder is
0.01 micrometer-2 micrometers are preferable. Oil absorption using DBP
The amount is 5-100ml / 100g, preferably 10-80
ml / 100 g, more preferably 20-60 ml / 10
It is appropriate to be 0 g. Specific gravity 1-12, preferred
3 to 6 is suitable. Shape is needle-like, sphere
, Polyhedron, or plate shape. The surface of these nonmagnetic powders is subjected to surface treatment.
By Al₂O_Three, SiO₂TiO₂, ZrO₂, Sn
O₂, Sb₂O_Three , ZnO is preferably present. Special
Preferred for dispersibility is Al.₂O_Three, SiO₂, Ti
O₂, ZrO₂More preferred is Al₂O_Three,
SiO₂, ZrO₂It is. Use these in combination
It can also be used alone. Also on purpose
A co-precipitated surface treatment layer may be used.
Those who treat the surface with silica after treatment with Lumina
Or vice versa. Also the table
The surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense is generally preferred. Known by mixing carbon black in the lower layer
Rs, which is the effect of
The micro Vickers hardness can be obtained. For this reason
There are furnace black for rubber and thermal black for rubber.
, Carbon black for color, acetylene black, etc.
Can be used. The specific surface area of carbon black is
100-500m²/ G, preferably 150-400m²
/ G, DBP oil absorption is 20-400ml / 100g, good
Preferably it is 30-200ml / 100g
It is. The average particle size of carbon black is 5 to 80 nm
(Mμ), preferred <10-50 nm (mμ), more preferred
10 to 40 nm (mμ) is appropriate.
The The carbon black has a pH of 2 to 10 and a water content of 0.
1-10%, tap density is preferably 0.1-1 g / ml
Yes. Specific examples of carbon black used in the present invention
As, BLACKPEARLS 2 manufactured by Cabot Corporation
000, 1300, 1000, 900, 800, 88
0, 700, VULCAN XC-72, Mitsubishi Chemical
# 3050B, 3150B, 3250B, # 375
0B, # 3950B, # 950, # 650B, # 970
B, # 850B, MA-600, Columbia Carbon
CONDUCTEX SC, RAVEN 8800,
8000, 7000, 5750, 5250, 3500,
2100, 2000, 1800, 1500, 1255,
1250, Akzo Ketchen Black EC, etc.
I can get lost. When the lower layer of the present invention is a magnetic layer, the magnetic powder
As a powder, γ-Fe₂O_ThreeCo-modified γ-Fe₂O_Three, Α
-Fe-based alloy, CrO₂Etc.
it can. In particular, Co-modified γ-Fe₂O_ThreeIs preferred. Main departure
The ferromagnetic powder used in the lower layer of the light is used in the upper magnetic layer.
It should have the same composition and performance as the ferromagnetic powder
Good. However, depending on the purpose, the performance changes in the upper and lower layers.
It is known in the art. For example, long wavelength recording characteristics
In order to improve the Hc of the lower magnetic layer, the upper magnetic layer
It is desirable to set it lower than that of
It is effective to make Br of the magnetic layer higher than that of the upper magnetic layer.
is there. In addition, the benefits of adopting a known multi-layer structure
Points can be given. A binder for the lower magnetic layer or the lower nonmagnetic layer,
Lubricants, dispersants, additives, solvents, dispersion methods, etc. are magnetic
It can be applied in layers. In particular, binder amount, type, addition
For the amount and type of additives and dispersants
Knowledge technology can be applied. Magnetic paint prepared by the above materials or non
A magnetic paint is applied on a nonmagnetic support to form a lower layer.
The non-magnetic support that can be used in the present invention is biaxial.
Stretched polyethylene naphthalate, polyethylene
Terephthalate, polyamide, polyimide, polyamide
Imide, aromatic polyamide, polybenzoxidazole
The well-known thing can be used. Preferably polyethylene
Examples include naphthalate and aromatic polyamide. these
The non-magnetic support of the corona discharge, plasma treatment
It is also possible to perform treatment, easy adhesion treatment, heat treatment or the like. The present invention
The nonmagnetic support that can be used for the centerline average surface
Roughness 0.1-20 at a cut-off value of 0.25 mm
Excellent smoothness in the range of nm, preferably 1-10 nm
It is preferable that the surface has properties. Also these
Nonmagnetic supports only have a low centerline average surface roughness.
In addition, it is preferable that there is no coarse protrusion of 1 μm or more. [Layer Structure] The magnetic recording medium of the present invention has a nonmagnetic support.
Lower layer (nonmagnetic layer or magnetic layer) and at least one on the holder
It is a multilayer structure having a magnetic layer. Fewer than the top magnetic layer
Simultaneously coat at least the upper magnetic layer adjacent to it
The binder of the present invention contained in the uppermost magnetic layer
Diffuses into the upper magnetic layer due to migration, etc.
In particular, the binder of the present invention is applied to an upper magnetic layer other than the uppermost magnetic layer.
Will be included. This effect is particularly effective with the upper magnetic layer.
This is remarkable when a thin magnetic layer is used. Upper magnetic layer
Is a single layer, the thickness is preferably 0.05 to 1.0 μm
Preferably, the thickness is 0.05 to 0.5 μm.
When the thickness of the uppermost magnetic layer is within the above range, smoothness and
A magnetic layer having high mechanical strength can be obtained. Also upper layer
When the magnetic layer is composed of multiple magnetic layers, it is located on the top layer
The thickness of the magnetic layer is 0.05 to 1.0 μm, preferably 0.
The upper magnetic layer is suitably from 0.5 to 0.5 μm.
The total thickness is 1.0 to 2.5 μm, preferably 1.0 to
It is appropriate that the thickness is 1.5 μm. The layer structure of the magnetic layer is
By being in the above range, smoothness and mechanical strength are high.
A magnetic layer can be obtained. The method of manufacturing the magnetic recording medium of the present invention is, for example,
For example, the coating liquid for the lower layer is applied to the surface of the non-magnetic support under running.
After or at the same time, apply magnetic paint to
So that the thickness of the magnetic layer after drying is equal to the preferred thickness of the magnetic layer.
The thickness after drying of the lower layer is 1.0 to 2.0 μm
More preferably, the thickness is 1.0 to 1.5 μm.
It is appropriate to apply as follows. As an application machine for applying the magnetic paint,
Air doctor coat, blade coat, rod coat
, Extrusion coating, air knife coating, squeeze coat
, Impregnation coat, reverse roll coat, transfer
-Roll coat, gravure coat, kiss coat, cast
To coat, spray coat, spin coat etc. are available
The For example, General Technology Center Co., Ltd.
Issued “Latest Coating Technology” (May 31, 1983
Day). Apparatus and method for applying the magnetic recording medium of the present invention
The following can be proposed as examples of the law. (1) Gravure generally applied in the application of magnetic paint,
For coating devices such as rolls, blades and extrusions
First, apply the lower layer, while the lower layer is in an undried state
Japanese Examined Patent Publication No. 1-46186, Japanese Patent Laid-Open No. 60-23817
9 and JP-A-2-265672.
Support-type extrusion coating device
To apply the upper layer. (2) JP-A-63-88080, JP-A-2-17
No. 971 and JP-A-2-265672.
One of the two coating liquid passage slits
The upper and lower layers are applied almost simultaneously by the application head. (3) It is disclosed in Japanese Patent Laid-Open No. 2-174965.
Extrusion coating with a backup roll like
The upper and lower layers are applied almost simultaneously with a cloth device. The nonmagnetic support magnetic coating used in the present invention is
Back layer (backing layer) is provided on the uncoated surface
It may be done. Usually, the back layer is a magnetic layer of a nonmagnetic support.
Abrasive material, antistatic agent, etc.
Back layer in which particulate components and binder are dispersed in organic solvent
It is a layer provided by applying a forming paint. Non-magnetic
Coating surface of support and magnetic coating and backcoat layer forming coating
An adhesive layer may be provided. Applied magnetic coating
The coating layer of the coating material is ferromagnetic powder contained in the coating layer of the magnetic paint.
The powder is dried after magnetic field orientation treatment. After being dried in this manner, it is applied to the coating layer.
It is preferable to perform a surface smoothing process. For surface smoothing
For example, a super calendar roll is used.
The By performing surface smoothing treatment, the solvent of the drying
The ferromagnetic powder in the magnetic layer disappears due to removal of vacancies
Magnetic recording with high electromagnetic conversion characteristics
A medium can be obtained. As a calendar processing role
Is epoxy, polyimide, polyamide, polyamide
Use heat-resistant plastic rolls such as Also metal
It can also be processed in rolls. Preferably metal roll
Is suitable. The magnetic recording medium of the present invention has a surface of a magnetic layer.
When the center line average roughness is 0.25 mm cut off
0.1 to 4 nm, preferably in the range of 1 to 3 nm
It is preferable that the surface has excellent smoothness.
For example, as described above, a specific ferromagnetic powder is used.
The magnetic layer formed by selecting the powder and the binder
This is done by applying Obtained magnetic recording medium
Cut into the desired size using a cutter etc.
can do. [0048] The following examples and comparative examples show the present invention.
Further details will be described. In the examples, “part” is indicated by “weight”.
Part ". [Polyurethane synthesis example] The diol components shown in Table 1 were refluxed.
Equipped with an air conditioner and a stirrer and placed in a container previously purged with nitrogen.
Dissolved in clohexanone 30% solution at 60 ° C under nitrogen flow
It was. Then, as a catalyst, dibutyltin dilaurate 60
ppm was added and dissolved for an additional 15 minutes. Further shown in Table 1
Add MDI and heat reaction at 90 ° C for 6 hours.
Resin solution A was obtained. Table in the same way as polyurethane A
Polyurethane BH is obtained with the raw materials and composition ratio shown in 1.
It was. Table 1 shows the molecular weight and Tg of the obtained polyurethane.
did. [Example 1] Ferromagnetic alloy powder (composition: Fe
89 atm%, Co 5 atm%, Y 6 atm%,
Hc 159 kA / m (2000 Oe), crystallite size
15nm, BET specific surface area 59m²/ G, major axis diameter 0.
12μm, acicular ratio 7, σ_S150A ・ m²/ Kg (150
emu / g)) 100 parts in an open kneader for 10 minutes
Grind and then 10 parts of polyurethane solution H (solid content)
Add 30 parts of cyclohexanone and mix for 60 minutes.
Kneaded. Then       Abrasive (Al₂O_Three, Particle size 0.3μm) 2 parts       Carbon black (particle size 40μm) 2 parts       Methyl ethyl ketone / toluene = 1/1 200 parts Was added and dispersed in a sand mill for 120 minutes. to this       Polyisocyanate 5 parts (solid content)       (Japan Polyurethane Coronate 3041)       Butyl stearate 2 parts       1 part of stearic acid       50 parts of methyl ethyl ketone After stirring for another 20 minutes, the average of 1 μm
Filter using a filter with a pore size and magnetic coating for the upper layer
The material was prepared. Α-Fe₂O_Three(Average particle size 0.15 μm, S
_BET52m²/ G, surface treatment Al₂O_Three, SiO₂, PH
6.5-8.0) 100 parts with an open kneader
Pulverize for minutes, then vinyl chloride / vinyl acetate / glycidyl methacrylate
Copolymer with 86/9/5
Compound added with sodium fonate salt (SO_ThreeNa =
6x10^-Fiveeq / g, epoxy = 10^-3eq / g, MW
 30,000) 7.5 parts and polyurethane H 10 parts (solid
Form) and 30 parts of cyclohexanone.
Kneaded for 0 minute. Then   Methyl ethyl ketone / cyclohexanone = 6/4 200 parts Was added and dispersed in a sand mill for 120 minutes. to this       Polyisocyanate 5 parts (solid content)       (Japan Polyurethane Coronate 3041)       Butyl stearate 2 parts       1 part of stearic acid       50 parts of methyl ethyl ketone After stirring for another 20 minutes, the average of 1 μm
Filter using a filter with a pore size,
Prepared. Next, sulfonic acid-containing polyester as an adhesive layer
Carry the tellurium so that the thickness after drying is 0.1 μm.
Apply to the surface of a 4 μm thick aramid support using luber
Clothed. Next, the obtained paint for the lower layer was further changed to 1.5 μm.
Immediately thereafter, the thickness after drying the upper magnetic coating was 0.05 μm.
m. Simultaneous multi-layer coating using reverse roll
did. Magnetic paint is applied to a non-magnetic support coated with magnetic paint.
Co magnet of 0.5T (5000 gauss) in the undried state
And 0.4T (4000 Gauss) solenoid magnet
Alignment and application of the metal roll-metal roll-
Metal roll-Metal roll-Metal roll-Metal roll-Gold
Calendar processing by combination of genus roll speed 100
m / min, linear pressure 2942 N / cm, temperature 90 ° C.
And then slit to a width of 3.8 mm. (Example 2-5 and Comparative Example 1-4) For upper layer
Table 2 shows polyurethane, lower layer polyurethane, and coating thickness.
Change as shown and create in the same way as in Example 1.
It was. (Example 6) α-Fe in the lower layer solution₂O_Three(average
Particle size 0.15μm, S_BET52m²/ G, surface treatment Al₂
O_Three, SiO₂PH 6.5-8.0) with titanium oxide (flat
Uniform grain size 0.035μm, crystalline rutile, TiO₂Content
90% or more, surface treatment layer alumina, S_BET35-42m²
/ G, true specific gravity 4.1, pH 6.5-8.0)
Was prepared in the same manner as in Example 2. Measuring method (1) Tg of polyurethane Dynamic viscoelasticity measuring device Leo Vibron manufactured by A & D
Measured at a frequency of 110 Hz and a heating rate of 2 ° C./min.
Then, the peak temperature of the loss modulus was obtained from (2) Weight average molecular weight of polyurethane THF solution using Tosoh high speed GPC HLC8020
Measured under the conditions of medium, flow rate 1 cc / min, detector RI,
It calculated | required in standard polystyrene conversion. (3) Number of minute protrusions Digital Instrument Nanoscope III (AFM: Atom
SiN probe with a ridge angle of 70 #
10μm square (100μm²) Minute protrusion height
The number of protrusions was measured every 5 nm up to 20 nm. (4) Electromagnetic conversion characteristics Single frequency signal of 4.7MHz with DDS4 drive
Recording was performed at the optimum recording current, and the reproduction output was measured. Comparison
The reproduction output of Example 1 is shown as a relative value with 0 dB. (5) Repeated coefficient of friction increase DDS4 drive with magnetic layer surface at 50 ° C and 20% RH
20g in contact with the guide pole used
(T1) is applied and the tension (T
2) Pull and pull the guide pole from T2 / T1
The friction coefficient of the magnetic surface was measured. Repeat measurement 100
1 until the first pass and the friction coefficient is 1.
The friction coefficient at the 000th pass was determined. (6) Coating film damage After the measurement of (5), the surface of the magnetic layer of the sample is subjected to a differential interference optical microscope.
And evaluated with the following ranks. Excellent: No scratches are seen. Good: Kiss is seen, but there are more parts without scratches. Bad: There are more scratched parts than scratchless parts
Yes. [0054] [Table 1] [0055] [Table 2]Evaluation results Polyureta having a glass transition temperature in the range of 100 to 200 ° C.
Is present in the uppermost magnetic layer.
The number of surface protrusions with a height of 10 to 20 nm is 5 to 1000/1.
00μm²Examples 1 to 6 within the range of
High reproducibility, little increase in coefficient of friction,
The running durability was good. The scope of the present invention
Use polyurethane with a Tg of over Tg for the top magnetic layer.
10-20 nm high surface present in the uppermost magnetic layer
Comparative example 1 in which the number of protrusions exceeds the range of the present invention is compared with the example.
The electromagnetic conversion characteristics were inferior. Present in the top magnetic layer
The number of surface protrusions with a height of 10 to 20 nm is within the scope of the present invention.
However, a polyurethane with a Tg lower than the scope of the present invention is the best.
Comparative Examples 2 and 3 used for the magnetic layer have good electromagnetic characteristics.
Although it was good, the coefficient of friction was greatly increased by repeated running.
As a result, the film damage after repeated running is high, and running durability
It was inferior. Polyureta contained in the uppermost magnetic layer
Tg is within the scope of the present invention.
The number of surface protrusions having a height of 10 to 20 nm exists within the scope of the present invention.
Comparative Example 4 exceeding the range is inferior to the example in terms of electromagnetic conversion characteristics.
In addition, after repeated running, scratches were observed on the coating surface. [0057] According to the present invention, the electromagnetic conversion characteristics are high and the repetition is high.
Less coating damage after running repeatedly and excellent running durability
Magnetic recording media can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J038 DG001 DG111 DG121 DG131                       DG261 HA066 HA216 KA08                       MA13 MA14 NA11 NA17 PB11                       PC08                 5D006 BA02 BA04 BA10 BA15 BA19

Claims (1)

What is claimed is: 1. A magnetic recording comprising a magnetic powder or a lower layer containing a nonmagnetic powder and a binder and at least one upper magnetic layer containing a ferromagnetic powder and a binder in this order on a nonmagnetic support. The medium, wherein at least the uppermost magnetic layer in the upper magnetic layer includes a binder including a polyurethane resin having a glass transition temperature in the range of 100 to 200 ° C., and is located in the uppermost layer. A magnetic recording medium, wherein the magnetic layer has 5 to 1000 surface protrusions having a height of 10 to 20 nm / 100 μm ^{2 on} the surface thereof.