JP2000331327A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a stable traveling property and excellent C/N and D. O.(dropout) characteristics of a magnetic recording medium. SOLUTION: This magnetic recording medium is constituted of a non- magnetic supporting body 1 which is provided on one side face of the supporting body with a magnetic layer 2 consisting of magnetic powder and a bonding agent each dispersed in a solvent and with non-magnetic layer 3 on the other side face of the supporting body. In this case, the composition and combination of three constituents of the non-magnetic layer 3, or carbon black, a polyurethane resin having a 20-70 deg.C glass transition temperature and containing tertiary amine and isocyanate type curable agent, are varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium having a magnetic layer on one main surface of a non-magnetic support and a non-magnetic layer on the other main surface of the non-magnetic support.

[0002]

2. Description of the Related Art Magnetic recording media are required to have improved characteristics as the performance of video tape recorders typified by high definition video tape recorders and digital video tape recorders increases. For this reason, development of a high-performance coating type magnetic recording medium has been actively studied. In recent years, as the recording wavelength has been shortened in order to increase the density and the capacity of a magnetic recording medium, the size of the magnetic powder used has also been reduced to fine particles.

As described above, the state of the surface of the magnetic layer of the magnetic recording medium, including the size of the magnetic powder contained in the magnetic paint, is very important in performing recording and reproduction. The phenomenon of dropout of signal during recording / reproduction (dropout, hereinafter referred to as DO) caused by adhesion of dust and dirt on the magnetic layer surface, agglomeration of magnetic paint components, or scratches or other defects on the medium surface This causes deterioration of the overall image quality.

[0004] In a conventional analog video tape recorder, D.I. O. Since the defect appears on the screen by the number of D. O. It is important to manufacture a magnetic recording medium having a small number of magnetic recording media.

There is a digital recording system as a recording system of a video signal. O. If there are many errors, the error rate will increase. For this reason, even in digital recording type magnetic recording media, D.I. O. Needs to be reduced.

[0006] The magnetic recording medium used in the above-described video tape recorder is formed in a tape shape, wound around a tape reel, and housed in a housing. Then, in the video tape recorder, the magnetic recording medium is rubbed against the magnetic head while traveling while being guided by the guide poles and the guide rollers. In the magnetic recording medium, recording and reproduction of an image are performed by a sliding magnetic head.

At this time, in order to reliably record and reproduce an image, the magnetic recording medium needs to have a uniform winding state on a tape reel without fluctuation in running speed, and to withstand repeated use. There is.

A magnetic recording medium that satisfies the above conditions usually has a high electric resistance of a magnetic layer, and thus generates static electricity when running at high speed. Therefore, it is desired that the surface properties of the magnetic recording medium that comes into contact with the guide poles and the like be in a state suitable for traveling and be a material having an antistatic effect.

In addition, the surface of the magnetic layer on the magnetic recording medium is
In order to improve the sensitivity, especially the output in the high frequency range, and to prevent the state of sliding of the magnetic recording medium on the magnetic head from fluctuating, the surface is finished smoothly. However, when the surface of the magnetic layer becomes extremely smooth, the dynamic frictional resistance increases, which tends to cause a problem in running properties of the magnetic recording medium.

When the housing containing the magnetic recording medium is mounted on a recording / reproducing apparatus such as a video tape recorder and run as described above, not only the front surface of the magnetic recording medium but also the back surface thereof are guided by guide poles. Or rubbed by the guide rollers. For this reason, when the running properties and durability of the back surface of the magnetic recording medium are not good, excessive tension is applied to the running magnetic recording medium, and the magnetic layer on the magnetic recording medium is excessively rubbed against the magnetic head. become.

If the magnetic layer is excessively rubbed against the magnetic head, there arises a problem that the magnetic layer is damaged and the magnetic powder in the magnetic layer comes off.

[0012] Further, the tension of the magnetic recording medium when it is wound up fluctuates, so that the winding pressure on the tape reel fluctuates. In this case, the winding shape of the magnetic recording medium is disturbed and the edges are uneven, so that the running of the magnetic recording medium becomes uneven during reuse. As a result, there arises a problem that an image such as skew, jitter and S / N or electromagnetic characteristics are deteriorated.

In order to improve these problems, it has been proposed to provide a back coat layer on the back surface of the magnetic recording medium. For example, there is a backcoat layer in which a resin layer containing an inorganic powder is formed on the main surface of a nonmagnetic support.

This is a method in which the coefficient of friction is reduced by making the surface of the back coat layer rough and reducing the contact area with a guide pole or the like. For example, JP
JP-A-7-130234, JP-A-58-161135, JP-A-57-53825, JP-A-58-2
No. 415 discloses an example using an inorganic powder.

As described in JP-B-52-17401, a magnetic recording medium having a back coat layer using carbon black instead of the above-mentioned inorganic powder has also been proposed. This aims at improving the antistatic and light-shielding effects by using the conductivity of carbon black and the improvement of the surface roughening effect by carbon black particles.

Further, as a means for reducing the frictional resistance of the back coat layer, a method has been devised in which a relatively small carbon black having an average primary particle size of 10 to 60 nm and a carbon black having an average primary particle size of 100 nm or more are used in combination. (JP-A-60-45938, JP-A-60-5959)
No. 39, No. 60-25023, No. 60-38
No. 725, No. 60-107729, No. 59-
Nos. 185027, 59-223937, 57-111828, and 50-147308).

[0017]

However, the surface of the back coat layer, which is the back surface of the magnetic recording medium (hereinafter referred to as the back surface), is, for example, in the state of being wound up like a video tape, at the surface of the magnetic recording medium. Direct contact with the surface of a certain magnetic layer (hereinafter referred to as a magnetic surface) may cause many adverse effects.

For example, when a back coating having a large surface roughness is applied in order to stabilize friction with a traveling system, magnetic properties are reduced due to stress relaxation (creeping phenomenon) caused by storing the wound state for a long time. This has a significant effect on the surface roughness of the layer. When the roughness of the magnetic layer is large, there is a problem that the electromagnetic conversion characteristics (particularly, C / N) are deteriorated due to generation of spacing loss between the magnetic layer and the magnetic head.

If coarse particles are present on the back surface, they may cause dents on the magnetic surface, or the particles may migrate from the back surface and adhere to the surface of the magnetic layer. O. In some cases. In particular, when a small amount of alumina, titanium oxide, or the like is added in addition to carbon black as the main component for the purpose of improving the durability of the back surface, migration of these particles from the back surface to the magnetic surface is likely to occur.

On the other hand, when the thickness of the back coat layer is about 1 μm, the particles contained in the back coat layer may have a size larger than the thickness of the back coat layer. In such a case, the coarse particles contained in the back coat layer are more likely to fall off. O. Cause an increase.

As described above, in the conventional magnetic recording medium, particles contained in the back coat layer may fall off and migrate to the magnetic layer, or the surface of the back coat layer may be transferred to the magnetic layer. there were. For this reason, the magnetic recording medium has excellent running durability, has improved magnetic conversion characteristics, and has a high D.O. O. There is a problem that the reduction of the amount cannot be achieved.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and ensures a stable running property, maintains the electromagnetic conversion characteristics and durability of the magnetic recording medium, and further improves the C value. / N characteristics and D.I. O. An object of the present invention is to provide a magnetic recording medium that can achieve characteristics.

[0023]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention comprises a non-magnetic support in which a magnetic powder and a binder are dispersed in a solvent on one surface of a non-magnetic support. In a magnetic recording medium formed of a magnetic layer coated with a magnetic paint and a non-magnetic layer coated with a non-magnetic paint on the other surface,
The non-magnetic layer is made of carbon black and 20 ° C. to 70 ° C.
A glass transition temperature (hereinafter referred to as Tg) exists between
A non-magnetic surface of the non-magnetic layer, comprising a polyurethane resin containing a tertiary amine as a polar group and an isocyanate-based curing agent, is measured with a contact-type surface roughness meter using a stylus having a contact-end radius of curvature of 2 μm. Center line average roughness (SRa)
Is 13 nm or more and 22 nm or less.

In the magnetic recording medium according to the present invention having the above-mentioned structure, friction of the surface of the nonmagnetic layer is reduced by using nonmagnetic carbon black having good dispersibility in the binder of the nonmagnetic layer. It is possible to stabilize. Further, by using a polyurethane resin containing a tertiary amine which is a polar group as a material of the non-magnetic layer, the carbon black can be dispersed well.

By using a polyurethane resin having a Tg between 20 ° C. and 70 ° C. as a binder, the non-magnetic layer has excellent surface roughness.

Further, by using an isocyanate-based curing agent, the nonmagnetic layer can have a desired hardness.

By defining the center line average roughness (SRa) on the surface of the nonmagnetic layer to be 13 nm or more and 22 nm or less, it is possible to obtain good electromagnetic conversion characteristics and D.I. O. It is intended to achieve the characteristics.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the magnetic recording medium according to the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the magnetic recording medium according to the present invention comprises a non-magnetic support 1, a magnetic layer 2 formed on one main surface 1a of the non-magnetic support 1, and a non-magnetic support. Support 1
And the non-magnetic layer 3 formed on the other main surface 1b.

In the magnetic recording medium, the nonmagnetic layer 3 is made of a nonmagnetic coating obtained by kneading carbon black, a polyurethane resin, and an isocyanate-based curing agent.
Formed on the other main surface 1b.

The carbon black that can be used for the non-magnetic layer 3 includes acetylene black and furnace black depending on the production method.

Here, in order to control the surface properties of the nonmagnetic layer 3 and stabilize the friction, a carbon black having a small particle diameter of 5 to 50 nm as carbon black and 200 nm
The above-mentioned large-diameter carbon can be mixed and used.

For the carbon black, for example, “Carbon Black Handbook (edited by Carbon Black Association)” can be referred to. Here, the carbon black has a DBP oil absorption of 30 to 150 ml / 100 g, preferably 50 to 150 ml / 100 g.
150 ml / 100 g, and the average particle diameter is 5
150 nm, preferably 15 to 50 nm, BET
Specific surface area by law, 40~300m ² / g, preferably effective ones is 100 to 250 m ² / g.
The tap density is 0.1 to 1 g / cc and the pH is
Is preferably 2.0 to 10.

Carbon black having a DBP oil absorption exceeding the above-mentioned range significantly deteriorates dispersibility,
The viscosity of the non-magnetic paint increases. If the DBP oil absorption is below the above range, the dispersibility deteriorates and the dispersion step takes time. The smaller the average particle diameter, the longer the dispersion time but the better the surface properties, and the larger the average particle diameter, the worse the surface properties. Therefore, the average particle diameter is preferably within the above range.

Examples of the carbon black satisfying the above conditions include, for example, Raven 1250 (particle size 23 nm, BET value 1) manufactured by Columbian Carbon Co., Ltd.
35.0 m ² / g, DBP oil absorption 58.0 ml / 100
g), raben 1255 (particle size 23 nm, BET value 12
5.0 m ² / g, DBP oil absorption 58.0 ml / 100
g), Raven 1020 (particle diameter 27 nm, BET value 9)
5.0 m ² / g, DBP oil absorption 60.0 ml / 100
g), Raven 1080 (particle size 28 nm, BET value 7)
8.0 m ² / g, DBP oil absorption 65.0 ml / 100
g), Raven 1035, Raven 1040, Raven 1060, Raven 3300, Raven 450, Raven 780, etc. and CONDUCTEX
SC (particle diameter 20 nm, BET value 220.0 m ² / g, D
BP oil absorption of 115.0 ml / 100 g). Asahi Carbon Co., Ltd. # 80 (particle size 23n
m, BET value 117.0 m ² / g, DBP oil absorption 11
3.0 ml / 100 g), Mitsubishi Chemical # 22B (particle size 4
0 nm, BET value 5.0 m ² / g, DBP oil absorption 13
1.0 ml / 100 g), # 20B (particle size 40 nm, B
ET value 56.0 m ² / g, DBP oil absorption 115.0 ml
/ 100g), Cabot Black Pearls (BL
ACKPEARLS) L (particle size 24 nm, BET value 25
0.0m ² / g, DBP oil absorption 60.0ml / 100
g), Black Pearls 800 (particle size: 17.0 nm, B
ET value 240.0 m ² / g, DBP oil absorption 75.0 ml
/ 100 g), Black Pearls 1000, Black Pearls 1100, Black Pearls 700, Black Pearls 905, and the like. MT carbon (Columbian Carbon Co., particle diameter 350 nm), Thermax M
T or the like can also be used.

The polyurethane resin used for the nonmagnetic layer 3 has a tertiary amine as a polar group. This polyurethane resin is a resin compound consisting of an active hydrogen compound and a diisocyanate. By combining these active hydrogen compounds and diisocyanates, which are raw materials, or changing the mixing ratio of both, a wide variety of characteristics can be freely designed. Has features that can be.

Specifically, the active hydrogen compound is mainly a glycol component, and depending on its type, there are polyester polyol, polyether polyol, polycaprolactone polyol, polycarbonate polyol and the like.
In addition, low molecular polyols, ie, water, ethylene glycol (EG), 1,3-propylene glycol (P
G), 1,2-PG, 1,4-butanediol (B
G), 1,5-pentane glycol, 1,6-hexanediol (HG), 3-methyl-1,5-pentane glycol, neopentyl glycol, 1,8-octane glycol, 1,9-nonanediol, diethylene glycol , Cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, dimer acid diol, trimethylolpropane (TMP), glycerin, hexanetriol, quadrol or bisphenol A
Of ethylene oxide or propylene oxide can also be used.

As the active hydrogen compound constituting the polyurethane resin, any of the polyols described above can be used. However, in consideration of long-term storage stability, a polyether-based or polycarbonate-based polyol that is difficult to hydrolyze is used. It is desirable to do.

As the diisocyanate which reacts with the polyol, for example, 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), xylene-1,4-diisocyanate, xylene -1,3-diisocyanate, 4,
4'-diphenylmethane diisocyanate (MDI),
2,4'-diphenylmethane diisocyanate-4,
4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2 '
-Diphenylpropane-4,4'-diisocyanate,
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate,
Aromatic diisocyanate such as 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, aliphatic diisocyanate such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), lysine diisocyanate, isophorone diisocyanate (IPD
I), aromatic diisocyanates such as hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and tetramethyl xylene diisocyanate.

The polyurethane resin can be synthesized by a solution synthesis method in which an active hydrogen compound as a raw material and a diisocyanate are reacted in an optional organic solvent. Further, the polyurethane resin can also be synthesized by a solid synthesis method in which an active hydrogen compound and a diisocyanate are directly mixed and reacted without using an organic solvent.

For example, in the solution synthesis method, an active hydrogen compound such as a polyol or glycol as a raw material of the polyurethane resin and a dissocyanate are mixed in an organic solvent capable of dissolving both of them. The polyurethane resin can be obtained by reacting.

On the other hand, in the solid synthesis method, a solid polyurethane resin can be obtained by mixing the above-mentioned active hydrogen compound and the above-mentioned diisocyanate with an extruder or a kneader and directly reacting them.

In this magnetic recording medium, even when carbon black having relatively low dispersibility is used, a polar group is contained as an active hydrogen compound as a raw material of the polyurethane resin in order to improve the dispersibility of the carbon black. A polar group is introduced into the polyurethane resin by using a compound having the above structure.

As the polar group to be introduced, a tertiary amine is used. Tertiary amines show more excellent properties when carbon black having a small particle size is dispersed, as compared with other polar groups such as sulfonates, carboxylic acids, and phosphoric acids. Further, it is more effective especially when the surface of the carbon black particles shows acidity.

Specifically, a tertiary amine-containing glycol is transesterified in a polyester such as butylene adipate, or caprolactone is added to the active hydrogen of the tertiary amine-containing glycol or the amine by several moles. A tertiary amine can be introduced into the polyurethane resin by performing a urethanization reaction using the polymer component obtained as a raw material.

The tertiary amine can be added to the polyurethane resin by directly performing a urethane reaction using a polar group-containing glycol compound, a polar group-containing amino alcohol compound or a polar group-containing diamine compound as a molecular chain extender. It can also be introduced.

The tertiary amine which can be used as the polar group-containing active hydrogen compound includes aliphatic amines, aromatic amines, alkanolamines and alkoxyalkylamines.

More specifically, the active hydrogen compound containing a polar group includes N-methyldiethanolamine (NMDE).
A), N-methyldiisopropylamine (NMDP
A), diethylaminopropanediol (DEAP)
D), N- (2-aminoethyl) ethanolamine, N
-Methylethanolamine, diisopropylamine, piperazine, 2-methyl-piperazine, (hydroxyethyl) piperazine, bis (aminopropyl) piperazine,
N-methylaniline, N-methylphenylamine and the like can be used.

The introduction amount of the above tertiary amine is 0.001 m
mol / g to 0.5 mmol / g is effective, and more preferably 0.05 mmol / g to 0.5 mmol / g. The introduction amount of the tertiary amine is 0.001 mmol /
When the amount is less than g, the dispersion effect of carbon black may be deteriorated. If the amount of the tertiary amine is more than 0.5 mmol / g, the viscosity of the polyurethane resin containing carbon black may increase, or the dispersion stability of carbon black may deteriorate. .

Next, the production of the polyurethane resin will be described in detail.

The polyurethane resin is obtained by reacting the above-mentioned diisocyanate component with the above-mentioned active hydrogen compound component such as polyester. At this time, it is preferable that the active hydrogen group excess condition be such that the equivalent ratio of the active hydrogen group in the active hydrogen compound component to the isocyanate group in the diisocyanate component exceeds 1.0. More preferably, the equivalent ratio of the active hydrogen group in the active hydrogen compound component to the isocyanate group is 1.0 to 2.0.

By setting the active hydrogen group excess condition, it is possible to make the polyurethane precursor contain active hydrogen groups without leaving any isocyanate groups in the produced polyurethane precursor.

When the equivalent ratio of the active hydrogen group in the active hydrogen compound component to the isocyanate group is less than 1.0 due to the difference in the reactivity of the reactive group contained in each molecule of the active hydrogen compound and the isocyanate, the polyurethane precursor There is a possibility that an active hydrogen group cannot be introduced into the polymer, and if it exceeds 2.0, the polyurethane precursor may gel.

The polyurethane resin can be produced by using the above-mentioned solid synthesis method in a molten state and a bulk state, and uniformly mixing and reacting the respective components at the above-mentioned equivalent ratio.

The reaction apparatus may be any apparatus, for example, a mixing and kneading apparatus such as a reaction vessel equipped with a stirrer, a kneader, and a single-screw or multi-screw extrusion reactor. In order to accelerate the reaction, a metal catalyst or an amine catalyst commonly used in the production of a polyurethane resin may be used as a catalyst.

The polyurethane resin used is a polyurethane resin having a number average molecular weight of 10,000 to 100,000, preferably a number average molecular weight of 10,000 to 70,000.
000, more preferably 20,000 to 6
It is 0000. Polyurethane resins having a number average molecular weight of more than 100,000 have poor solution handling due to high solution viscosity.

Further, the Tg of the polyurethane resin is 20 ° C.
７０70 ° C. Specifically, the Tg of the polyurethane resin can be controlled by the following method. When the molecular weight of the active hydrogen compound decreases, the concentration of urethane bonds increases and the cohesion between molecules increases, so that the Tg of the polyurethane resin increases. Alternatively, the Tg of the polyurethane resin can be increased by using an aromatic polyol or diisocyanate rather than an aliphatic one.

If the Tg is lower than 20 ° C., the hardness of the surface of the nonmagnetic layer 3 becomes soft, so that the surface property is deteriorated during the mirror surface treatment (calendering) of the surface of the magnetic layer 2 or when the magnetic layer 2 is stored for a long time. In addition, for example, when stored in a wound state like a video tape, there arises a problem that the surface of the nonmagnetic layer 3 and the surface of the magnetic layer 2 adhere to each other.

When the Tg is higher than 70 ° C., the surface of the nonmagnetic layer 3 becomes hard, so that the flexibility is lowered and the contact with the guide roller or the like on the recording / reproducing apparatus side may be deteriorated. On the other hand, if the Tg is higher than 70 ° C., the adhesion to the non-magnetic support 1 deteriorates, and the reactivity with the isocyanate compound used as a curing agent decreases. Therefore, the Tg of the polyurethane resin is from 20C to 70C, and preferably from 40C to 60C.

The non-magnetic layer 3 contains an isocyanate compound as a curing agent. By including the isocyanate-based curing agent in the nonmagnetic layer 3, the durability of the nonmagnetic layer 3 can be improved. The isocyanate-based curing agent can further improve the durability of the nonmagnetic layer 3 by setting the average number of functional groups to 2 or more.

As the isocyanate-based curing agent, a polymer of polyisocyanate, a polyol adduct of polyisocyanate, and the like can be suitably used. Above all, isocyanurate having a cyclic skeleton, which is a trimer of diisocyanate, is a curing agent having higher reactivity and is effective in improving durability.

As the isocyanate-based curing agent,
An aromatic polyisocyanate and an aliphatic polyisocyanate are mentioned, and an adduct of both of these and an active hydrogen compound is preferred.

For example, as the aromatic polyisocyanate, toluene diisocyanate (TDI), 1,3-
Xylene diisocyanate, 1,4-xylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl diisocyanate and the like can be mentioned.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, and isophorone diisocyanate (IP
DI) and the like.

The active hydrogen compound which forms an adduct with both the above-mentioned aromatic polyisocyanate and the above-mentioned aliphatic polyisocyanate includes ethylene glycol,
There are 4-butanediol, 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane, glycerin and the like.
Those having a range of 00 to 5,000 are preferred.

The amount of the isocyanate-based curing agent added is
It is at most 20 parts by weight, preferably at most 10 parts by weight, relative to the active hydrogen compound.

Theoretically, a sufficient amount of isocyanate-based curing agent is added so that the active hydrogen groups in the polyurethane resin composition (or the binder resin composition) are equivalent to the isocyanate groups. However, in the actual production of a polyurethane resin, the isocyanate in the isocyanate-based curing agent reacts and is lost under the influence of moisture and the like, so that an amount of isocyanate equivalent to the active hydrogen group is insufficient. For this reason, 10% or more of the active hydrogen group equivalent
A 50% excess of isocyanate-based curing agent is added.

Further, when a curing agent comprising a polyisocyanate is used, after coating with a magnetic paint,
By promoting the curing reaction at a temperature of 0 ° C. to 80 ° C. for several hours, stronger adhesiveness can be obtained.

Next, the roughness of the surface of the nonmagnetic layer 3 will be described. The surface roughness of the nonmagnetic layer 3 is 13 nm or more and 22 nm or less in center line average roughness (SRa) measured by a contact type surface roughness meter with a stylus having a contact end curvature radius of 2 μm.

When SRa is less than 13 nm, the friction becomes small, and the running property deteriorates. On the other hand, when SRa is more than 22 nm, for example, when the film is wound like a video tape, it comes into direct contact with the surface of the magnetic layer 2 which is the surface of the magnetic recording medium. Due to the stress relaxation (creeping phenomenon), the surface properties of the magnetic layer 2 are deteriorated.

Therefore, by setting SRa within the above range, excellent running properties, excellent electromagnetic conversion characteristics, and D.C. O. And a magnetic recording medium with a small amount of noise can be obtained.

By setting the ten-point average roughness (SRz), which indicates the ratio of large projections, to 250 nm or more, it is possible to reduce winding disturbance in the step of winding the magnetic recording medium into the housing (winding step). When SRz is less than 250 nm, there are few large projections, so that friction increases and air escape during the winder process becomes poor, resulting in a magnetic recording medium in which turbulence is likely to occur.

Here, the center line average roughness (SRa) and the 10-point average roughness (SRz) measured by the contact type surface roughness meter are determined by JI.
The surface roughness is measured according to SB0601, and is measured from the vertical displacement of a contact when a stylus having a contact end radius of curvature of 2 μm is slid on the surface to be measured.

The surface roughness of the nonmagnetic layer 3 can be controlled by adjusting the combination of carbon blacks having different particle diameters and the dispersibility of the carbon black in the polyurethane resin.

However, in this magnetic recording medium, not only the surface roughness is controlled by the combination of carbon blacks having different particle diameters and the dispersibility of the carbon black in the polyurethane resin, but also the
The surface roughness can be controlled by using a polyurethane resin having a Tg in the range of up to 70 ° C. and changing the conditions of the calendar (pressure, temperature, processing speed) to achieve the optimum surface roughness. It becomes possible.

Solvents for preparing non-magnetic paints and magnetic paints include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethyl acetate monoacetate. Ester solvents such as ethyl ether, glycol ether solvents such as glycol monoethyl ether and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chloromethane Chlorine-containing solvents such as hydrin and dichlorobenzene are exemplified. In addition, other conventionally known organic solvents can be used.

In addition, in this magnetic recording medium, a binder, an abrasive, an antistatic agent, an antirust agent, or a magnetic paint other than the ferromagnetic powder mixed in the nonmagnetic support 1 and the magnetic layer 2 is prepared. Any known solvent can be used without any limitation.

As the ferromagnetic powder, γ-FeOx (x =
1.33 to 1.5), Co-modified γ-FeOx (x = 1.
33-1.5), known ferromagnetic materials such as a ferromagnetic alloy containing Fe, Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite.

In addition, these ferromagnetic powders include Al, Si, S, Sc, Ti, V, Cr, Cu,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ni, Ta, W, Re, Au, Hg, Pb, Bi,
It may contain atoms such as La, Ce, P, Mn, Zn, Co, Sr, and B.

A more useful ferromagnetic powder is a ferromagnetic grain metal powder, and σs = 100 Am ² / kg to ²⁰⁰ Am ²
/ Kg, and the specific surface area by the BET method is 45 to 60 m
² / g and a coercive force of 90 kA / m to 200 kA / m shows a remarkable effect.

As the material of the nonmagnetic support 1, those generally used for magnetic recording media can be used.
For example, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyethylene, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, cellulose derivatives such as cellulose acetate butyrate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, Examples include polycarbonate, polyimide, polyamideimide, other plastics, metals such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon.

Among them, the nonmagnetic support 1 includes polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer which is supposed to impart flexibility, and cellulose derivative, phenol resin, epoxy resin which is supposed to impart rigidity. It is desirable to use a resin or the like.

As the binder used for the magnetic layer 3, any known material can be used. That is, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Coalescence, acrylate-vinylidene chloride copolymer, acrylate-
Acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer , Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea For example, a formaldehyde resin, a polyvinyl acetal resin, or a mixture thereof is used.

The above-mentioned binder may be one into which a suitable polar group has been introduced.

Examples of the non-magnetic powder that can be used for the magnetic layer 2 include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide having an α conversion of 90% or more. Corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide,
Raw materials for magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, and magnetic iron oxide are dehydrated and annealed acicular α-iron oxide, and if necessary, Those surface-treated with aluminum and / or silica are used alone or in combination.

The particle size of the nonmagnetic powder is usually 0.01
To 2 μm, preferably 0.015 to 1.00 μm
It is more preferably 0.015 to 0.50 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have the same effect by widening the particle size distribution. You can also.

The tap density of the non-magnetic powder is usually 0.05
To 2 g / cc, preferably 0.2 to 1.5 g / c
c. The specific surface area is usually 1 to 200 m ² / g, preferably 5 to 100 m ² / g, and more preferably 7 to 80 m ² / g. The crystallite size is usually 0.01 to 2 μm, preferably 0.015 to 1.
00 μm, more preferably 0.015 to 0.50
μm.

The DBP oil absorption of the nonmagnetic powder is usually 5 to 1
00ml / 100g, preferably 10-80ml
/ 100g, more preferably 20-60ml / 1
00 g. The specific gravity is usually from 1 to 12, preferably from 2 to 8.

The shape of the nonmagnetic powder may be any of a needle shape, a spherical shape, a die shape, and a plate shape, and is not particularly limited.

The above non-magnetic powder does not necessarily have to be 100% pure, and the surface may be treated with another compound according to the purpose. At that time, if the purity is usually 70% or more, the effect is not reduced. For example, when using titanium oxide as the non-magnetic powder, the surface of the titanium oxide may be treated with alumina.

It is desirable that the nonmagnetic powder has a loss on ignition of 20% or less and a Mohs hardness of 6 or more.

For example, a Mohs hardness of 6 containing α-alumina, β-alumina, fused alumina, titanium oxide or the like as a main component.
The above known materials can be used alone or in combination as a non-magnetic powder.

As a concrete example, UA56 manufactured by Showa Denko
00, UA5605, Sumitomo Chemical AKP-20, AKP
-30, AKP-50, HIT-50, HIT-10
0, ZA-G1, N5, G7, S-
1. Toda Kogyo-mori, TF-100, TF-120, TF
-140, DPN250BX, DBN270BX, TTO-51B, TO-55A, TTO-55 manufactured by Ishihara Sangyo
B, TTO-55C, TTO-55S, TTO-55
D, FT-1000, FT-2000, FTL-10
0, FTL-200, M-1, S-1, SN-100,
TCT 52, STT-4D, STT-3
0D, STT-30, STT-65C, T-1 manufactured by Mitsubishi Materials, NS-O, NS-3Y, NS-8 manufactured by Nippon Shokubai
Y, Teika MT-100S, MT-100T, MT-
150W, MT-500B, MT-600B, MT-1
00F, Saine Chemical Fine X-25, BF-1, BF
-10, BF-20, BF-1L, BF-10P, DEFIC-Y and DEFIC-R manufactured by Dowa Mining Co., Ltd., and Y-LOP manufactured by Titanium Industry.

Known lubricants can be used. For example, higher fatty acid esters, silicone oils, fatty acid-modified silicones, fluorine-containing silicones, or other fluorine-based lubricants, polyolefins, polyglycols, alkyl phosphates and metal salts, polyphenyl ethers, fluorinated alkyl ethers, alkyl carboxylic acids Amine-based lubricants such as amine salts and amine salts of fluorinated alkylcarboxylic acids, alcohols having 12 to 24 carbon atoms (each of which may contain an unsaturated bond or may be branched), and those having 12 to 24 carbon atoms; Higher fatty acids and the like can be used.

The higher fatty acid ester component includes
Higher fatty esters having 12 to 32 carbon atoms (each of which may contain an unsaturated bond or may be branched), for example, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, Examples include methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, pentyl ester, hexyl ester, heptyl ester, octyl ester and the like such as oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid and linoleic acid.

Specific compound names include butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, butoxyethyl stearate, octyl myristate, isooctyl myristate, butyl palmitate and the like. . Further, the lubricant may be used as a mixture with a plurality of lubricants.

As the antistatic agent, in addition to the above-mentioned carbon black, known antistatic agents such as natural surfactants, nonionic surfactants, and cationic surfactants can be used.

The magnetic layer 2 and the non-magnetic layer 3 of this magnetic recording medium
In both cases, a known coupling agent may be used.
As the coupling agent, a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, or the like can be used. Here, the addition amount of the coupling agent with respect to 100 parts by weight of the magnetic material is 0.05%.
Parts to 10.00 parts, more preferably 0.1 to 5.00 parts.

Examples of the silane coupling agent include vinyl silane compounds such as γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane, and β- (3,
Epoxysilane compounds such as 4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimexisilane And a mercaptosilane compound such as γ-mercaptopropyltrimethoxysilane can be suitably used.

As titanate coupling agents, tetra-n-butoxytitanium, tetraisopropoxytitanium, bis [2-[(2-aminoethyl) amino] ethanolate] [2-[(2-aminoethyl) amino) Ethanolate-O] (2-propanolate) titanium, tris (isooctadecanoate-O) (2-propanolate) titanium, bis (ditridecylphosphite)
O ") tetrakis (2-propanolate) dihydrozentitanate, bis (dioctylphosphite-O")
Tetrakis (2-propanolate) dihydrozentitanate, tris (dioctylphosphite-O ″) (2
-Propanolate) titanium, bis (dioctylphosphite-O ″) [1,2-ethanediolate (2-)
-O, O '] titanium, tris (dodecylbenzenesulfonate-O) (2-propanolate) titanium, tetrakis [2,2-bis [(2-propenyloxy) methyl] -1-butanolate titanate and the like are used. it can.

[0101] Commercially available products include Ajinomoto Co., Inc., Prenact KR TTS, KR 46B, KR 55, KR 41
B, KR 38S, KR 138S, KR 238S,
338X, KR 12, KR 44, KR 9SA, K
R34S and the like can be suitably used.

As the aluminum-based coupling agent,
Acetoalkoxyaluminum diisopropylate and the like.
LM and the like can be suitably used.

As a method for preparing the magnetic paint and the non-magnetic paint, any known method can be used. For example,
Roll mills, ball mills, sand mills, tron mills, high-speed stone mills, basket mills, dispersers, homomixers, kneaders, continuous kneaders, extruders, homogenizers, ultrasonic dispersers, and the like can be used.

When applying the magnetic paint and the non-magnetic paint, the corona discharge treatment on the undercoat layer such as an adhesive layer or the non-magnetic support 1 is performed before the application directly onto the non-magnetic support 1. Or a pretreatment such as an electron beam irradiation treatment.

The method of applying the magnetic paint and the non-magnetic paint on the non-magnetic support 1 includes air doctor coating,
Examples of the method include a blade coat, a rod coat, an extrusion coat, an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a transfer roll coat, and a cast coat.

A method other than those described above can be used, and furthermore, simultaneous multilayer coating by extrusion coating may be used.

Here, in some cases, the non-magnetic support 1 and the non-magnetic layer 2
A layer (undercoat layer) containing the above-mentioned known binder as a main component may be provided.

[0108]

EXAMPLES Examples of the present invention and comparative examples will be described in detail, but the present invention is not limited to these examples. Unless otherwise specified, parts and% in Examples
Means “parts by weight” and “% by weight”, respectively.

Example 1 In Example 1, a coating material for a magnetic layer and a coating material for a nonmagnetic layer were prepared according to the following composition.

<Preparation of paint for magnetic layer> Composition of paint for magnetic layer Metal magnetic powder 100 parts (σs = 150 Am ² / kg, Hc = 130 kA / m) (Specific surface area by BET method: 55 m ² / g) PVC copolymer 15 parts (trade name: MR-110, manufactured by Nippon Zeon Co., Ltd.) 5 parts polyester polyurethane resin (isophthalic acid / terephthalic acid / butanediol-MDI-based polyurethane, molecular weight 25,000, polar group: SO ₃ Na = 0.2 wt%) α-Al ₂ O ₃ 10 parts (Sumitomo Chemical Co., trade name HIT-50) Carbon black 1 part (Cabot Co., trade name BP-L) Polyisocyanate 4 parts (Nippon Polyurethane Co., trade name Coronate L) Myristic acid 1 Part butyl stearate 1 part methyl ethyl ketone 80 parts methyl isobutyl ketone 80 parts toluene 8 After kneading the magnetic layer coating composition parts described above in a continuous kneader,
Dispersed using a sand mill. Thereafter, 4 parts of polyisocyanate and 1 part of myristic acid were added, and the mixture was filtered through a filter having an average diameter of 1 μm to obtain a coating material for a magnetic layer.

<Preparation of Non-Magnetic Layer Coating Composition> Non-magnetic layer coating composition Carbon black (average particle diameter: 20 nm) 100 parts Carbon black (average particle diameter: 350 nm) 5 parts Polyurethane resin Variable amount shown in Tables 1 and 2 Polyisocyanate 5 parts (manufactured by Nippon Polyurethane Co., Ltd., trade name: Coronate L) 180 parts of methyl ethyl ketone 180 parts of methyl isobutyl ketone 180 parts of toluene The above-mentioned coating composition for a non-magnetic layer was dispersed using a sand mill, and 5 parts of polyisocyanate was added thereto. The mixture was filtered through a filter having an average diameter to obtain a coating for a non-magnetic layer.

The above coating material for a nonmagnetic layer was applied to a polyethylene terephthalate film having a thickness of 10 μm to a thickness of 0.8 μm, and dried. Next, a magnetic paint was applied to the surface opposite to the non-magnetic layer in a thickness of 4.0 μm and dried. afterwards,
It was calendered and kept at 60 ° C. for 20 hours for curing. The wide magnetic film obtained in this way is reduced by half.
It was cut to inch width. Also, insert this into a cartridge (HD
(For CAM (trade name)) to produce a magnetic recording medium.

Examples 2 to 10 In Examples 2 to 10, a non-magnetic layer was formed using a polyurethane resin as shown in Table 1, and the non-magnetic layer was subjected to calendar conditions and center line average roughness. A magnetic recording medium was manufactured in the same manner as in Example 1 except that (SRa) was adjusted as shown in Table 1.

[0114]

[Table 1]

Comparative Examples 1 to 18 In Comparative Examples 1 to 18, a non-magnetic layer was formed using a polyurethane resin as shown in Table 2, and the non-magnetic layer was subjected to calendar conditions and center line average roughness. A magnetic recording medium was manufactured in the same manner as in Example 1 except that (SRa) was adjusted as shown in Table 2.

However, in Comparative Example 4, Comparative Example 4 shown in Table 2 was used.
The components other than 5 were not kneaded, dissolved in a disper, and then dispersed in a sand mill.

[0117]

[Table 2]

Incidentally, with respect to Examples 1 to 10 and Comparative Examples 1 to 18 described above,
"Surface roughness", "Tg of polyurethane resin", "electromagnetic conversion characteristics", "rolled shape", and "adhesion" were measured.

<Measurement Method> (1) Measurement of Surface Roughness The surface roughness of the nonmagnetic layer was measured under the following conditions in accordance with JIS-B0601. In addition, the sample was measured at n = 3 and the average value was obtained.

Measuring instrument ET-30HK Manufacturer Kosaka Laboratory Measurement conditions Contact probe method with contact end curvature radius of 2 μm Measurement range 250 μ × 50 μ Height magnification × 50.000 Cutoff 80

(2) Measurement of Tg of Polyurethane Resin A polyurethane resin liquid (solid content: about 30 wt%) was applied on release paper to a thickness of about 30 to 50 μm, and dried at 60 ° C. for 1 hour. Thereafter, the film was further dried at 120 ° C. for 2 hours to produce a clear film. OR each clear film
Dynamic viscoelasticity analyzer (RHEOVIB) manufactured by IENTEC
RON MODEL RHEO-2000) at a measurement frequency of 35 Hz and a heating rate of 2.0 ° C./min to obtain Tg.

(3) Electromagnetic conversion characteristics The electromagnetic conversion characteristics include reproduction output, C / N and D.E. O.
Was measured and evaluated. As a reproduction output, a recording / reproducing apparatus (manufactured by Sony Corporation, trade name: HDWS-500) was used.
The output at 6.98 MHz was measured as a relative output with the output of Comparative Example 1 set to 0 dB. Also, as C / N,
The value at +1.0 MHz was measured. D. O. As a recording / reproducing apparatus (manufactured by Sony Corporation, trade name DVW-50)
0) and a VTR dropout counter (SHlb
The number of missing signals of −6 dB, 3 μsec or more was measured by ASOKU. In addition, D. O. The number of
If the number is 100 or less per minute, it is good, and 500
Exceeding the number may cause trouble.

(4) Winding figure Betacam video tape winder, tension 12
The film was wound at 0 gf and 6 m / s. The roll appearance at this time was evaluated according to the following criteria. ：: No pattern on the winding surface, clean state △: Pattern on the winding surface ×: Step on the winding surface

(5) Adhesion The above magnetic film cut into a 1/2 inch width was wound about 240 m on a metal reel and boiled in a water bath at 80 ° C. for 2 hours. Then, it was dried for 24 hours and measured according to the following criteria. O: No adhesion between the magnetic surface and the non-magnetic surface. Δ: One with peeling of the coating film on the magnetic surface or the non-magnetic surface. X: Adhesion between the magnetic surface and the non-magnetic surface. "Electromagnetic conversion characteristics" in Examples 1 to 10;
Table 3 shows the evaluation results of the “winding appearance” and “adhesion”, and Table 4 shows the evaluation results of “electromagnetic conversion characteristics”, “winding appearance”, and “adhesion” for Comparative Examples 1 to 18.

[0125]

[Table 3]

[0126]

[Table 4]

As can be seen from Tables 3 and 4,
Examples 1 to 3 show the measurement results when the Tg of a polyurethane resin in which a diethylamino group was introduced as a polar group was changed. When Tg is in the range of 20 ° C to 70 ° C, C
/ N, D. O. Both show that a good magnetic recording medium is obtained. On the other hand, in Comparative Examples 11 and 12 produced using the same polyurethane resin as that used in Example 2 and changing only the calendar conditions, when the calendar pressure was reduced, the C / N deteriorated, and the calendar pressure decreased. Is too large, the SRz becomes small, the friction increases, and the running property of the magnetic recording medium deteriorates. As a result, the winding appearance deteriorates.

In Comparative Examples 9 and 10 produced by changing both the Tg and the calendar conditions of the polyurethane resin used in Examples 1 to 3, the SRz value was 250.
nm or less, and the friction was increased, so that the winding appearance was disturbed. In Comparative Example 9, sticking also occurred.

Examples 4 to 6 are the results of similar evaluations of the polyurethane resins used in Examples 1 to 3 in which only the amount of the polar group was changed.

On the other hand, in Comparative Example 13 produced by changing the Tg of the polyurethane resin used in Example 4 to 10 ° C., it can be seen that the winding appearance is disturbed and sticking occurs. Also,
In Comparative Example 14 in which the Tg of the polyurethane resin used in Example 4 was changed to 80 ° C. and the calendar temperature was increased, the value of SRz was 250 nm or less, and the friction increased. It turns out that it becomes.

Examples 7 to 10 show the results when the same measurement was performed using a polyurethane resin having a diethylaminopropyl group as a polar group while changing both Tg and calendar conditions. Here, comparing Example 7 and Example 8, it can be seen that even when the same polyurethane resin is used, the C / N changes when the calendar conditions are changed. In addition, it can be seen that when SRz is 250 nm or more, the winding appearance becomes good.

Comparative Examples 17 and 18 are the same as those in Example 9.
It was prepared by changing only the calendar conditions of the polyurethane resin used in the above. When the calendar pressure is increased, the SRz is reduced, so that the friction is increased. As a result, the running property of the magnetic recording medium is deteriorated, and as a result, the winding appearance is deteriorated.
It can be seen that the value of SRa decreases when the calendar pressure is low and the calendar temperature is low.

In Comparative Examples 15 and 16 produced by changing both the Tg and the calendar conditions of the polyurethane resin used in Examples 7 to 10, the SRz value was 2
It can be seen that, since the friction becomes large at 50 nm or less, the winding appearance is disturbed, and in Comparative Example 15, sticking occurs.

In particular, when Comparative Examples 1 to 8 are compared with all examples using a polyurethane resin containing a tertiary amine-based polar group, the polyurethane resin containing a tertiary amine-based polar group is compared. When used, D.I. O. It can be seen that is improved.

[0135]

According to the present invention, a stable running property is ensured, the electromagnetic conversion characteristics and the durability of the magnetic recording medium are maintained, and a more favorable C / N characteristic and D.C. O. It is possible to provide a magnetic recording medium that can achieve the characteristics.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part showing an example of the configuration of a magnetic recording medium according to the present invention.

[Explanation of symbols]

 1 Non-magnetic support, 2 Magnetic layer, 3 Non-magnetic layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Kawamura 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Reiko Watanabe 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F term (reference) 5D006 CC01 CC02 CC03 FA05 FA09

Claims (2)

[Claims] 1. A magnetic layer formed by applying a magnetic paint obtained by dispersing a magnetic powder and a binder in a solvent to one surface of a nonmagnetic support, and a nonmagnetic paint applied to the other surface. In a magnetic recording medium having a non-magnetic layer, the non-magnetic layer comprises carbon black and 20 ° C. to 70 ° C.
A polyurethane resin containing a tertiary amine as a polar group and a isocyanate-based curing agent, wherein the surface of the nonmagnetic layer has a contact end radius of curvature of 2 μm. Center line average roughness (S
A magnetic recording medium wherein Ra) is 13 nm or more and 22 nm or less. 2. The magnetic recording medium according to claim 1, wherein a ten-point average roughness (SRz) on the nonmagnetic surface is 250 nm or more.